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class="vector-toc-list"> <li id="toc-Thread_angle" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Thread_angle"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.1</span> <span>Thread angle</span> </div> </a> <ul id="toc-Thread_angle-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Types_of_threads" class="vector-toc-list-item vector-toc-level-2"> <a class="vector-toc-link" href="#Types_of_threads"> <div class="vector-toc-text"> <span class="vector-toc-numb">4.2</span> <span>Types of threads</span> </div> </a> <ul id="toc-Types_of_threads-sublist" class="vector-toc-list"> </ul> </li> </ul> </li> <li id="toc-Uses" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Uses"> <div class="vector-toc-text"> <span class="vector-toc-numb">5</span> <span>Uses</span> </div> </a> <ul id="toc-Uses-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Distance_moved" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Distance_moved"> <div class="vector-toc-text"> <span class="vector-toc-numb">6</span> <span>Distance moved</span> </div> </a> <ul id="toc-Distance_moved-sublist" class="vector-toc-list"> </ul> </li> <li id="toc-Frictionless_mechanical_advantage" class="vector-toc-list-item vector-toc-level-1 vector-toc-list-item-expanded"> <a class="vector-toc-link" href="#Frictionless_mechanical_advantage"> <div class="vector-toc-text"> <span class="vector-toc-numb">7</span> <span>Frictionless mechanical advantage</span> </div> </a> <button aria-controls="toc-Frictionless_mechanical_advantage-sublist" class="cdx-button cdx-button--weight-quiet cdx-button--icon-only vector-toc-toggle"> <span class="vector-icon mw-ui-icon-wikimedia-expand"></span> <span>Toggle Frictionless mechanical advantage subsection</span> </button> <ul id="toc-Frictionless_mechanical_advantage-sublist" 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class="interlanguage-link-target"><span>Български</span></a></li><li class="interlanguage-link interwiki-de mw-list-item"><a href="https://de.wikipedia.org/wiki/Gewinde" title="Gewinde – German" lang="de" hreflang="de" data-title="Gewinde" data-language-autonym="Deutsch" data-language-local-name="German" class="interlanguage-link-target"><span>Deutsch</span></a></li><li class="interlanguage-link interwiki-es mw-list-item"><a href="https://es.wikipedia.org/wiki/Tuerca_de_tornillo_de_potencia" title="Tuerca de tornillo de potencia – Spanish" lang="es" hreflang="es" data-title="Tuerca de tornillo de potencia" data-language-autonym="Español" data-language-local-name="Spanish" class="interlanguage-link-target"><span>Español</span></a></li><li class="interlanguage-link interwiki-fa mw-list-item"><a href="https://fa.wikipedia.org/wiki/%D9%BE%DB%8C%DA%86_(%D9%85%D8%A7%D8%B4%DB%8C%D9%86_%D8%B3%D8%A7%D8%AF%D9%87)" title="پیچ (ماشین ساده) – Persian" lang="fa" hreflang="fa" data-title="پیچ (ماشین 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</div> </div> <div id="bodyContent" class="vector-body" aria-labelledby="firstHeading" data-mw-ve-target-container> <div class="vector-body-before-content"> <div class="mw-indicators"> </div> <div id="siteSub" class="noprint">From Wikipedia, the free encyclopedia</div> </div> <div id="contentSub"><div id="mw-content-subtitle"><span class="mw-redirectedfrom">(Redirected from <a href="/w/index.php?title=Screw_(simple_machine)&redirect=no" class="mw-redirect" title="Screw (simple machine)">Screw (simple machine)</a>)</span></div></div> <div id="mw-content-text" class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div class="shortdescription nomobile noexcerpt noprint searchaux" style="display:none">Mechanism that converts motion, and forces, from rotational to linear</div> <style data-mw-deduplicate="TemplateStyles:r1236090951">.mw-parser-output .hatnote{font-style:italic}.mw-parser-output div.hatnote{padding-left:1.6em;margin-bottom:0.5em}.mw-parser-output .hatnote i{font-style:normal}.mw-parser-output .hatnote+link+.hatnote{margin-top:-0.5em}@media print{body.ns-0 .mw-parser-output .hatnote{display:none!important}}</style><div role="note" class="hatnote navigation-not-searchable">For the screw as a fastener, see <a href="/wiki/Screw" title="Screw">screw</a>. For other uses, see <a href="/wiki/Screw_(disambiguation)" class="mw-disambig" title="Screw (disambiguation)">screw (disambiguation)</a>.</div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:GearBoxRotLinScrew.gif" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/7/7f/GearBoxRotLinScrew.gif/220px-GearBoxRotLinScrew.gif" decoding="async" width="220" height="89" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/7/7f/GearBoxRotLinScrew.gif/330px-GearBoxRotLinScrew.gif 1.5x, //upload.wikimedia.org/wikipedia/commons/7/7f/GearBoxRotLinScrew.gif 2x" data-file-width="397" data-file-height="160" /></a><figcaption>Animation showing the operation of a screw. As the screw shaft rotates, the <a href="/wiki/Nut_(hardware)" title="Nut (hardware)">nut</a> moves linearly along the shaft. This is a type called a <a href="/wiki/Lead_screw" class="mw-redirect" title="Lead screw">lead screw</a>.</figcaption></figure> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Screw_demonstrator.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/32/Screw_demonstrator.png/220px-Screw_demonstrator.png" decoding="async" width="220" height="143" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/32/Screw_demonstrator.png/330px-Screw_demonstrator.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/32/Screw_demonstrator.png/440px-Screw_demonstrator.png 2x" data-file-width="538" data-file-height="350" /></a><figcaption>A machine used in schools to demonstrate the action of a screw, from 1912. It consists of a threaded shaft through a threaded hole in a stationary mount. When the crank on the right is turned, the shaft moves horizontally through the hole.</figcaption></figure> <p>The <b>screw</b> is a mechanism that converts <a href="/wiki/Rotation" title="Rotation">rotational</a> motion to <a href="/wiki/Linear_motion" title="Linear motion">linear motion</a>, and a <a href="/wiki/Torque" title="Torque">torque</a> (rotational force) to a linear <a href="/wiki/Force" title="Force">force</a>.<sup id="cite_ref-Young_1-0" class="reference"><a href="#cite_note-Young-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> It is one of the six classical <a href="/wiki/Simple_machine" title="Simple machine">simple machines</a>. The most common form consists of a cylindrical shaft with <a href="/wiki/Helix" title="Helix">helical</a> grooves or ridges called <i><a href="/wiki/Screw_thread" title="Screw thread">threads</a></i> around the outside.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> The screw passes through a hole in another object or medium, with threads on the inside of the hole that mesh with the screw's threads. When the shaft of the screw is rotated relative to the stationary threads, the screw moves along its axis relative to the medium surrounding it; for example rotating a <a href="/wiki/Wood_screw" class="mw-redirect" title="Wood screw">wood screw</a> forces it into wood. In screw mechanisms, either the screw shaft can rotate through a threaded hole in a stationary object, or a threaded collar such as a <a href="/wiki/Nut_(hardware)" title="Nut (hardware)">nut</a> can rotate around a stationary screw shaft.<sup id="cite_ref-Collins_4-0" class="reference"><a href="#cite_note-Collins-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Bhandari_5-0" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Geometrically, a screw can be viewed as a narrow <a href="/wiki/Inclined_plane" title="Inclined plane">inclined plane</a> wrapped around a <a href="/wiki/Cylinder_(geometry)" class="mw-redirect" title="Cylinder (geometry)">cylinder</a>.<sup id="cite_ref-Young_1-1" class="reference"><a href="#cite_note-Young-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> </p><p>Like the other simple machines a screw can amplify force; a small rotational force (<a href="/wiki/Torque" title="Torque">torque</a>) on the shaft can exert a large axial force on a load. The smaller the <a href="/wiki/Pitch_(screw)" class="mw-redirect" title="Pitch (screw)">pitch</a> (the distance between the screw's threads), the greater the <a href="/wiki/Mechanical_advantage" title="Mechanical advantage">mechanical advantage</a> (the ratio of output to input force). Screws are widely used in <a href="/wiki/Threaded_fastener" class="mw-redirect" title="Threaded fastener">threaded fasteners</a> to hold objects together, and in devices such as <a href="/wiki/Screw_top" class="mw-redirect" title="Screw top">screw tops</a> for containers, <a href="/wiki/Vise" title="Vise">vises</a>, <a href="/wiki/Screw_jack" class="mw-redirect" title="Screw jack">screw jacks</a> and <a href="/wiki/Screw_press" title="Screw press">screw presses</a>. </p><p>Other mechanisms that use the same principle, also called screws, do not necessarily have a shaft or threads. For example, a <a href="/wiki/Corkscrew" title="Corkscrew">corkscrew</a> is a helix-shaped rod with a sharp point, and an <a href="/wiki/Archimedes%27_screw" title="Archimedes' screw">Archimedes' screw</a> is a water pump that uses a rotating helical chamber to move water uphill. The common principle of all screws is that a rotating <a href="/wiki/Helix" title="Helix">helix</a> can cause linear motion. </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="History">History</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=1" title="Edit section: History"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Restored_olive_press_from_the_Roman_Empire.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Restored_olive_press_from_the_Roman_Empire.jpg/220px-Restored_olive_press_from_the_Roman_Empire.jpg" decoding="async" width="220" height="165" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Restored_olive_press_from_the_Roman_Empire.jpg/330px-Restored_olive_press_from_the_Roman_Empire.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/e/e7/Restored_olive_press_from_the_Roman_Empire.jpg/440px-Restored_olive_press_from_the_Roman_Empire.jpg 2x" data-file-width="480" data-file-height="360" /></a><figcaption>Wooden screw in ancient Roman olive press</figcaption></figure> <p>The screw was one of the last of the simple machines to be invented.<sup id="cite_ref-Woods_6-0" class="reference"><a href="#cite_note-Woods-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup> It first appeared in <a href="/wiki/Mesopotamia" title="Mesopotamia">Mesopotamia</a> during the <a href="/wiki/Neo-Assyrian" class="mw-redirect" title="Neo-Assyrian">Neo-Assyrian</a> period (911-609) BC,<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup> and then later appeared in <a href="/wiki/Ancient_Egypt" title="Ancient Egypt">Ancient Egypt</a> and <a href="/wiki/Ancient_Greece" title="Ancient Greece">Ancient Greece</a>.<sup id="cite_ref-Bunch_8-0" class="reference"><a href="#cite_note-Bunch-8"><span class="cite-bracket">[</span>8<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Krebs_9-0" class="reference"><a href="#cite_note-Krebs-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup> </p><p>Records indicate that the <a href="/wiki/Water_screw" class="mw-redirect" title="Water screw">water screw</a>, or <a href="/wiki/Screw_pump" title="Screw pump">screw pump</a>, was first used in Ancient Egypt,<sup id="cite_ref-Britannica_10-0" class="reference"><a href="#cite_note-Britannica-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Stewart_11-0" class="reference"><a href="#cite_note-Stewart-11"><span class="cite-bracket">[</span>11<span class="cite-bracket">]</span></a></sup> some time before the Greek philosopher <a href="/wiki/Archimedes" title="Archimedes">Archimedes</a> described the <a href="/wiki/Archimedes_screw" class="mw-redirect" title="Archimedes screw">Archimedes screw</a> water pump around 234 BC.<sup id="cite_ref-Haven_12-0" class="reference"><a href="#cite_note-Haven-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> Archimedes wrote the earliest theoretical study of the screw as a machine,<sup id="cite_ref-13" class="reference"><a href="#cite_note-13"><span class="cite-bracket">[</span>13<span class="cite-bracket">]</span></a></sup> and is considered to have introduced the screw in Ancient Greece.<sup id="cite_ref-Krebs_9-1" class="reference"><a href="#cite_note-Krebs-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Kerle_14-0" class="reference"><a href="#cite_note-Kerle-14"><span class="cite-bracket">[</span>14<span class="cite-bracket">]</span></a></sup> By the first century BC, the screw was used in the form of the <a href="/wiki/Screw_press" title="Screw press">screw press</a> and the Archimedes' screw.<sup id="cite_ref-Britannica_10-1" class="reference"><a href="#cite_note-Britannica-10"><span class="cite-bracket">[</span>10<span class="cite-bracket">]</span></a></sup> </p><p>Greek philosophers defined the screw as one of the <a href="/wiki/Simple_machine" title="Simple machine">simple machines</a> and could calculate its (ideal) <a href="/wiki/Mechanical_advantage" title="Mechanical advantage">mechanical advantage</a>.<sup id="cite_ref-Usher_15-0" class="reference"><a href="#cite_note-Usher-15"><span class="cite-bracket">[</span>15<span class="cite-bracket">]</span></a></sup> For example, <a href="/wiki/Heron_of_Alexandria" class="mw-redirect" title="Heron of Alexandria">Heron of Alexandria</a> (52 AD) listed the screw as one of the five mechanisms that could "set a load in motion", defined it as an <a href="/wiki/Inclined_plane" title="Inclined plane">inclined plane</a> wrapped around a cylinder, and described its fabrication and uses,<sup id="cite_ref-Laufer1915_16-0" class="reference"><a href="#cite_note-Laufer1915-16"><span class="cite-bracket">[</span>16<span class="cite-bracket">]</span></a></sup> including describing a <a href="/wiki/Taps_and_dies" class="mw-redirect" title="Taps and dies">tap</a> for cutting female screw threads.<sup id="cite_ref-17" class="reference"><a href="#cite_note-17"><span class="cite-bracket">[</span>17<span class="cite-bracket">]</span></a></sup> </p><p>Because their complicated helical shape had to be laboriously cut by hand, screws were only used as linkages in a few machines in the ancient world. Screw fasteners only began to be used in the 15th century in clocks, after <a href="/wiki/Screw-cutting_lathe" title="Screw-cutting lathe">screw-cutting lathes</a> were developed.<sup id="cite_ref-18" class="reference"><a href="#cite_note-18"><span class="cite-bracket">[</span>18<span class="cite-bracket">]</span></a></sup> The screw was also apparently applied to drilling and moving materials (besides water) around this time, when images of <a href="/wiki/Auger_(drill)" class="mw-redirect" title="Auger (drill)">augers</a> and drills began to appear in European paintings.<sup id="cite_ref-Haven_12-1" class="reference"><a href="#cite_note-Haven-12"><span class="cite-bracket">[</span>12<span class="cite-bracket">]</span></a></sup> The complete dynamic theory of simple machines, including the screw, was worked out by Italian scientist <a href="/wiki/Galileo_Galilei" title="Galileo Galilei">Galileo Galilei</a> in 1600 in <i>Le Meccaniche</i> ("On Mechanics").<sup id="cite_ref-Krebs_9-2" class="reference"><a href="#cite_note-Krebs-9"><span class="cite-bracket">[</span>9<span class="cite-bracket">]</span></a></sup><sup class="reference nowrap"><span title="Page / location: 163">: 163 </span></sup><sup id="cite_ref-Stephen_19-0" class="reference"><a href="#cite_note-Stephen-19"><span class="cite-bracket">[</span>19<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Lead_and_pitch">Lead and pitch</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=2" title="Edit section: Lead and pitch"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Lead_and_pitch_in_screws.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Lead_and_pitch_in_screws.png/330px-Lead_and_pitch_in_screws.png" decoding="async" width="330" height="175" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Lead_and_pitch_in_screws.png/495px-Lead_and_pitch_in_screws.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/2e/Lead_and_pitch_in_screws.png/660px-Lead_and_pitch_in_screws.png 2x" data-file-width="724" data-file-height="384" /></a><figcaption>Lead and pitch are the same in single-start screws, but differ in multiple-start screws</figcaption></figure> <p>The fineness or coarseness of a screw's threads are defined by two closely related quantities:<sup id="cite_ref-Bhandari_5-1" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <ul><li>The <i><a href="/wiki/Lead_(engineering)" title="Lead (engineering)">lead</a></i> is defined as the axial distance (parallel to the screw's axis) the screw travels in one complete revolution (360°) of the shaft. The lead determines the <a href="/wiki/Mechanical_advantage" title="Mechanical advantage">mechanical advantage</a> of the screw; the smaller the lead, the higher the mechanical advantage.<sup id="cite_ref-20" class="reference"><a href="#cite_note-20"><span class="cite-bracket">[</span>20<span class="cite-bracket">]</span></a></sup></li> <li>The <i><a href="/wiki/Screw_thread#Lead,_pitch,_and_starts" title="Screw thread">pitch</a></i> is defined as the axial distance between the crests of adjacent threads.</li></ul> <p>In most screws, called "<i>single start</i>" screws, which have a single helical thread wrapped around them, the lead and pitch are equal. They only differ in "<i>multiple start</i>" screws, which have several intertwined threads. In these screws the lead is equal to the pitch multiplied by the number of <i>starts</i>. Multiple-start screws are used when a large linear motion for a given rotation is desired, for example in <a href="/wiki/Screw_cap" title="Screw cap">screw caps</a> on bottles, and <a href="/wiki/Ball_point_pen" class="mw-redirect" title="Ball point pen">ball point pens</a>. </p> <div class="mw-heading mw-heading2"><h2 id="Handedness">Handedness</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=3" title="Edit section: Handedness"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Screw_thread_handedness.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Screw_thread_handedness.png/220px-Screw_thread_handedness.png" decoding="async" width="220" height="222" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Screw_thread_handedness.png/330px-Screw_thread_handedness.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Screw_thread_handedness.png/440px-Screw_thread_handedness.png 2x" data-file-width="513" data-file-height="517" /></a><figcaption>Right-hand and left-hand screw threads</figcaption></figure> <p>The helix of a screw's thread can twist in two possible directions, which is known as <i><a href="/wiki/Handedness" title="Handedness">handedness</a></i>. Most screw threads are oriented so that when seen from above, the screw shaft moves away from the viewer (the screw is tightened) when turned in a <a href="/wiki/Clockwise" title="Clockwise">clockwise</a> direction.<sup id="cite_ref-McManus_21-0" class="reference"><a href="#cite_note-McManus-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Anderson_22-0" class="reference"><a href="#cite_note-Anderson-22"><span class="cite-bracket">[</span>22<span class="cite-bracket">]</span></a></sup> This is known as a <i>right-handed</i> (<i>RH</i>) thread, because it follows the <a href="/wiki/Right_hand_grip_rule" class="mw-redirect" title="Right hand grip rule">right hand grip rule</a>: when the fingers of the right hand are curled around the shaft in the direction of rotation, the thumb will point in the direction of motion of the shaft. Threads oriented in the opposite direction are known as <i>left-handed</i> (<i>LH</i>). </p><p>By common convention, right-handedness is the default handedness for screw threads.<sup id="cite_ref-McManus_21-1" class="reference"><a href="#cite_note-McManus-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> Therefore, most threaded parts and fasteners have right-handed threads. One explanation for why right-handed threads became standard is that for a <a href="/wiki/Right-handedness" class="mw-redirect" title="Right-handedness">right-handed</a> person, tightening a right-handed screw with a <a href="/wiki/Screwdriver" title="Screwdriver">screwdriver</a> is easier than tightening a left-handed screw, because it uses the stronger <a href="/wiki/Supinator_muscle" title="Supinator muscle">supinator muscle</a> of the arm rather than the weaker <a href="/wiki/Pronation" class="mw-redirect" title="Pronation">pronator</a> muscle.<sup id="cite_ref-McManus_21-2" class="reference"><a href="#cite_note-McManus-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup> Since most people are right-handed, right-handed threads became standard on threaded fasteners. </p><p>Screw linkages in machines are exceptions; they can be right- or left-handed depending on which is more applicable. Left-handed screw threads are also used in some other applications: </p> <ul><li>Where the rotation of a shaft would cause a conventional right-handed nut to loosen rather than to tighten due to <a href="/wiki/Precession_(mechanical)" title="Precession (mechanical)">fretting induced precession</a>. Examples include: <ul><li>The <a href="/wiki/Bicycle_pedal" title="Bicycle pedal">left hand pedal</a> on a <a href="/wiki/Bicycle" title="Bicycle">bicycle</a>.<sup id="cite_ref-McManus_21-3" class="reference"><a href="#cite_note-McManus-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-23" class="reference"><a href="#cite_note-23"><span class="cite-bracket">[</span>23<span class="cite-bracket">]</span></a></sup></li> <li>The left-hand screw holding a <a href="/wiki/Circular_saw" title="Circular saw">circular saw</a> blade or a <a href="/wiki/Bench_grinder" title="Bench grinder">bench grinder</a> wheel on.</li></ul></li> <li>In some devices that have threads on either end, like <a href="/wiki/Turnbuckle" title="Turnbuckle">turnbuckles</a> and removable pipe segments. These parts have one right-handed and one left-handed thread, so that turning the piece tightens or loosens both threads at the same time.</li> <li>In some gas supply connections to prevent dangerous misconnections. For example, in gas welding the flammable gas supply line is attached with left-handed threads, so it will not be accidentally switched with the oxygen supply, which uses right-handed threads.</li> <li>To make them useless to the public (thus discouraging theft), left-handed <a href="/wiki/Light_bulb" class="mw-redirect" title="Light bulb">light bulbs</a> are used in some railway and <a href="/wiki/Subway_station" class="mw-redirect" title="Subway station">subway stations</a>.<sup id="cite_ref-McManus_21-4" class="reference"><a href="#cite_note-McManus-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup></li> <li>Coffin lids are said to have been traditionally held on with left-handed screws.<sup id="cite_ref-McManus_21-5" class="reference"><a href="#cite_note-McManus-21"><span class="cite-bracket">[</span>21<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Cook_24-0" class="reference"><a href="#cite_note-Cook-24"><span class="cite-bracket">[</span>24<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Oakley_25-0" class="reference"><a href="#cite_note-Oakley-25"><span class="cite-bracket">[</span>25<span class="cite-bracket">]</span></a></sup></li></ul> <div class="mw-heading mw-heading2"><h2 id="Screw_threads">Screw threads</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=4" title="Edit section: Screw threads"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main articles: <a href="/wiki/Screw_thread" title="Screw thread">Screw thread</a> and <a href="/wiki/Metric_thread" class="mw-redirect" title="Metric thread">Metric thread</a></div> <p>Different shapes (profiles) of threads are used in screws employed for different purposes. Screw threads are standardized so that parts made by different manufacturers will mate correctly. </p> <div class="mw-heading mw-heading3"><h3 id="Thread_angle">Thread angle</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=5" title="Edit section: Thread angle"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Thread_angle" title="Thread angle">Thread angle</a></div> <p>The <i>thread angle</i> is the included <a href="/wiki/Angle" title="Angle">angle</a>, measured at a section parallel to the axis, between the two bearing faces of the thread. The angle between the axial load force and the normal to the bearing surface is approximately equal to half the thread angle, so the thread angle has a great effect on the friction and efficiency of a screw, as well as the wear rate and the strength. The greater the thread angle, the greater the angle between the load vector and the surface normal, so the larger the <a href="/wiki/Normal_force" title="Normal force">normal force</a> between the threads required to support a given load. Therefore, increasing the thread angle increases the friction and wear of a screw. </p><p>The outward facing angled thread bearing surface, when acted on by the load force, also applies a radial (outward) force to the nut, causing <a href="/wiki/Tensile_stress" class="mw-redirect" title="Tensile stress">tensile stress</a>. This radial <i>bursting force</i> increases with increasing thread angle. If the tensile strength of the nut material is insufficient, an excessive load on a nut with a large thread angle can split the nut. </p><p>The thread angle also has an effect on the strength of the threads; threads with a large angle have a wide root compared with their size and are stronger. </p> <figure class="mw-default-size mw-halign-center" typeof="mw:File/Thumb"><a href="/wiki/File:Screw_thread_forms.png" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/3/33/Screw_thread_forms.png/590px-Screw_thread_forms.png" decoding="async" width="590" height="173" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/3/33/Screw_thread_forms.png/885px-Screw_thread_forms.png 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/3/33/Screw_thread_forms.png/1180px-Screw_thread_forms.png 2x" data-file-width="1272" data-file-height="372" /></a><figcaption>Standard types of screw threads: (a) V, (b) American National, (c) British Standard, (d) Square, (e) Acme, (f) Buttress, (g) Knuckle</figcaption></figure> <div class="mw-heading mw-heading3"><h3 id="Types_of_threads">Types of threads</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=6" title="Edit section: Types of threads"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>In <a href="/wiki/Threaded_fastener" class="mw-redirect" title="Threaded fastener">threaded fasteners</a>, large amounts of friction are acceptable and usually wanted, to prevent the fastener from unscrewing.<sup id="cite_ref-Bhandari_5-2" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> So threads used in fasteners usually have a large 60° thread angle: </p> <ul><li><b>(a) V thread</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Self-tapping_screw" title="Self-tapping screw">Self-tapping screw</a></div> - These are used in <a href="/wiki/Self-tapping_screw" title="Self-tapping screw">self-tapping screws</a> such as wood screws and sheet metal screws which require a sharp edge to cut a hole, and where additional friction is needed to make sure the screw remains motionless, such as in <a href="/wiki/Setscrew" class="mw-redirect" title="Setscrew">setscrews</a> and adjustment screws, and where the joint must be fluid tight as in <a href="/wiki/Threaded_pipe" title="Threaded pipe">threaded pipe</a> joints.</li> <li><b>(b) American National</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Further information: <a href="/wiki/National_pipe_thread" title="National pipe thread">National pipe thread</a></div> - This has been replaced by the almost identical <a href="/wiki/Unified_Thread_Standard" title="Unified Thread Standard">Unified Thread Standard</a>. It has the same 60° thread angle as the V thread but is stronger because of the flat root. Used in bolts, nuts, and a wide variety of fasteners.</li> <li><b>(c) Metric thread</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Metric_thread" class="mw-redirect" title="Metric thread">Metric thread</a></div> - These threads are specified and common for ISO and DIN standards.</li> <li><b>(d) Whitworth</b> or <b>British Standard</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/British_Standard_Whitworth" title="British Standard Whitworth">British Standard Whitworth</a></div> - Very similar British standard replaced by the <a href="/wiki/Unified_Thread_Standard" title="Unified Thread Standard">Unified Thread Standard</a>.</li></ul> <p>In machine linkages such as <a href="/wiki/Lead_screw" class="mw-redirect" title="Lead screw">lead screws</a> or <a href="/wiki/Jackscrew" title="Jackscrew">jackscrews</a>, in contrast, friction must be minimized.<sup id="cite_ref-Bhandari_5-3" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> Therefore, threads with smaller angles are used: </p> <ul><li><b>(e) Square thread</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Square_thread" class="mw-redirect" title="Square thread">Square thread</a></div> - This is the strongest and lowest friction thread, with a 0° thread angle,<sup id="cite_ref-Bhandari_5-4" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> and does not apply bursting force to the nut. However it is difficult to fabricate, requiring a single point cutting tool due to the need to undercut the edges.<sup id="cite_ref-Bhandari_5-5" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> It is used in high-load applications such as <a href="/wiki/Jackscrew" title="Jackscrew">jackscrews</a> and <a href="/wiki/Lead_screw" class="mw-redirect" title="Lead screw">lead screws</a> but has been mostly replaced by the Acme thread. A <i>modified square thread</i> with a small 5° thread angle is sometimes used instead, which is cheaper to manufacture.</li> <li><b>(f) Acme thread</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Acme_thread" class="mw-redirect" title="Acme thread">Acme thread</a></div> - With its 28° thread angle this has higher friction than the square thread, but is easier to manufacture and can be used with a <a href="/wiki/Split_nut" title="Split nut">split nut</a> to adjust for wear.<sup id="cite_ref-Bhandari_5-6" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> It is widely used in <a href="/wiki/Vise" title="Vise">vises</a>, <a href="/wiki/C-clamp" title="C-clamp">C-clamps</a>, <a href="/wiki/Valve" title="Valve">valves</a>, <a href="/wiki/Scissor_jack" class="mw-redirect" title="Scissor jack">scissor jacks</a> and <a href="/wiki/Lead_screw" class="mw-redirect" title="Lead screw">lead screws</a> in machines like lathes.</li> <li><b>(g) Buttress thread</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Buttress_thread" title="Buttress thread">Buttress thread</a></div> - This is used in high-load applications in which the load force is applied in only one direction, such as <a href="/wiki/Screw_jack" class="mw-redirect" title="Screw jack">screw jacks</a>.<sup id="cite_ref-Bhandari_5-7" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> With a 0° angle of the bearing surface it is as efficient as the square thread but stronger and easier to manufacture.</li> <li><b>(h) Knuckle thread</b> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1236090951"><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="/wiki/Knuckle_thread" title="Knuckle thread">Knuckle thread</a></div> - Similar to a square thread in which the corners have been rounded to protect them from damage, also giving it higher friction. In low-strength applications it can be manufactured cheaply from sheet stock by <a href="/wiki/Rolling_(metalworking)" title="Rolling (metalworking)">rolling</a>. It is used in <a href="/wiki/Light_bulb" class="mw-redirect" title="Light bulb">light bulbs</a> and sockets.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Uses">Uses</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=7" title="Edit section: Uses"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif/220px-Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif" decoding="async" width="220" height="159" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/2/22/Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif/330px-Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/2/22/Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif/440px-Archimedes-screw_one-screw-threads_with-ball_3D-view_animated_small.gif 2x" data-file-width="505" data-file-height="365" /></a><figcaption>A <a href="/wiki/Screw_conveyor" title="Screw conveyor">screw conveyor</a> uses a rotating helical screw blade to move bulk materials.</figcaption></figure> <ul><li>Because of its self-locking property (see below) the screw is widely used in <a href="/wiki/Threaded_fastener" class="mw-redirect" title="Threaded fastener">threaded fasteners</a> to hold objects or materials together: the <a href="/wiki/Wood_screw" class="mw-redirect" title="Wood screw">wood screw</a>, <a href="/wiki/Sheet_metal_screw" class="mw-redirect" title="Sheet metal screw">sheet metal screw</a>, <a href="/wiki/Stud_welding" title="Stud welding">stud</a>, and <a href="/wiki/Screw" title="Screw">bolt</a> and <a href="/wiki/Nut_(hardware)" title="Nut (hardware)">nut</a>.</li> <li>The self-locking property is also key to the screw's use in a wide range of other applications, such as the <a href="/wiki/Corkscrew" title="Corkscrew">corkscrew</a>, <a href="/wiki/Screw_top" class="mw-redirect" title="Screw top">screw top</a> container lid, <a href="/wiki/Threaded_pipe" title="Threaded pipe">threaded pipe</a> joint, <a href="/wiki/Vise" title="Vise">vise</a>, <a href="/wiki/C-clamp" title="C-clamp">C-clamp</a>, and <a href="/wiki/Screw_jack" class="mw-redirect" title="Screw jack">screw jack</a>.</li> <li>Screws are also used as linkages in machines to transfer power, in the <a href="/wiki/Worm_gear" class="mw-redirect" title="Worm gear">worm gear</a>, <a href="/wiki/Lead_screw" class="mw-redirect" title="Lead screw">lead screw</a>, <a href="/wiki/Ball_screw" title="Ball screw">ball screw</a>, and <a href="/wiki/Roller_screw" title="Roller screw">roller screw</a>. Due to their low efficiency, screw linkages are seldom used to carry high power, but are more often employed in low power, intermittent uses such as positioning <a href="/wiki/Actuator" title="Actuator">actuators</a>.</li> <li>Rotating helical screw blades or chambers are used to move material in the <a href="/wiki/Archimedes%27_screw" title="Archimedes' screw">Archimedes' screw</a>, <a href="/wiki/Auger_(drill)" class="mw-redirect" title="Auger (drill)">auger earth drill</a>, and <a href="/wiki/Screw_conveyor" title="Screw conveyor">screw conveyor</a>.</li> <li>The <a href="/wiki/Micrometer_(device)" title="Micrometer (device)">micrometer</a> uses a precision calibrated screw for measuring lengths with great accuracy.</li></ul> <p>The <a href="/wiki/Screw_propeller" class="mw-redirect" title="Screw propeller">screw propeller</a>, although it shares the name <i>screw</i>, works on very different physical principles from the above types of screw, and the information in this article is not applicable to it. </p> <div class="mw-heading mw-heading2"><h2 id="Distance_moved">Distance moved</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=8" title="Edit section: Distance moved"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The linear distance <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle d\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>d</mi> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle d\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/0f203b686a923982358b9274fb508753ac31b996" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.603ex; height:2.176ex;" alt="{\displaystyle d\,}"></span> a screw shaft moves when it is rotated through an angle of <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \alpha \,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>α</mi> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \alpha \,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/652e1fd9c3a2ca00e1a517783cdbb0e18e4181f8" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.875ex; height:1.676ex;" alt="{\displaystyle \alpha \,}"></span> degrees is: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle d=l{\frac {\alpha }{360^{\circ }}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>d</mi> <mo>=</mo> <mi>l</mi> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>α</mi> <msup> <mn>360</mn> <mrow class="MJX-TeXAtom-ORD"> <mo>∘</mo> </mrow> </msup> </mfrac> </mrow> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle d=l{\frac {\alpha }{360^{\circ }}}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/2161732aa49d78d7006ddd0b2a6ae2fc0eace5c5" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.005ex; width:10.772ex; height:4.843ex;" alt="{\displaystyle d=l{\frac {\alpha }{360^{\circ }}}\,}"></span></dd></dl> <p>where <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle l\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>l</mi> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle l\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/db8b3f411aa6977b35e33fffcd39d6713bf4e46b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.08ex; height:2.176ex;" alt="{\displaystyle l\,}"></span> is the lead of the screw. </p><p>The <i>distance ratio</i> of a <a href="/wiki/Simple_machine" title="Simple machine">simple machine</a> is defined as the ratio of the distance the applied force moves to the distance the load moves. For a screw it is the ratio of the circular distance <i>d<sub>in</sub></i> a point on the edge of the shaft moves to the linear distance <i>d<sub>out</sub></i> the shaft moves. If <i>r</i> is the radius of the shaft, in one turn a point on the screw's rim moves a distance of 2π<i>r</i>, while its shaft moves linearly by the lead distance <i>l</i>. So the distance ratio is </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\mbox{distance ratio}}\equiv {\frac {d_{in}}{d_{out}}}={\frac {2\pi r}{l}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="false" scriptlevel="0"> <mtext>distance ratio</mtext> </mstyle> </mrow> <mo>≡</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>2</mn> <mi>π</mi> <mi>r</mi> </mrow> <mi>l</mi> </mfrac> </mrow> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\mbox{distance ratio}}\equiv {\frac {d_{in}}{d_{out}}}={\frac {2\pi r}{l}}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/547eba85bff87e2f16da4e3989db3fcfac3ae223" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.338ex; width:29.221ex; height:5.843ex;" alt="{\displaystyle {\mbox{distance ratio}}\equiv {\frac {d_{in}}{d_{out}}}={\frac {2\pi r}{l}}\,}"></span></dd></dl> <div class="mw-heading mw-heading2"><h2 id="Frictionless_mechanical_advantage">Frictionless mechanical advantage</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=9" title="Edit section: Frictionless mechanical advantage"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:House_Jack_2.5_tons.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/House_Jack_2.5_tons.jpg/220px-House_Jack_2.5_tons.jpg" decoding="async" width="220" height="293" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/1/1c/House_Jack_2.5_tons.jpg/330px-House_Jack_2.5_tons.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/1/1c/House_Jack_2.5_tons.jpg/440px-House_Jack_2.5_tons.jpg 2x" data-file-width="1536" data-file-height="2048" /></a><figcaption>A <a href="/wiki/Screw_jack" class="mw-redirect" title="Screw jack">screw jack</a>. When a bar is inserted in the holes at top and turned it can raise a load</figcaption></figure> <p>The <a href="/wiki/Mechanical_advantage" title="Mechanical advantage">mechanical advantage</a> <i>MA</i> of a screw is defined as the ratio of axial output force <i>F<sub>out</sub></i> applied by the shaft on a load to the rotational force <i>F<sub>in</sub></i> applied to the rim of the shaft to turn it. For a screw with no <a href="/wiki/Friction" title="Friction">friction</a> (also called an <i>ideal screw</i>), from <a href="/wiki/Conservation_of_energy" title="Conservation of energy">conservation of energy</a> the work done <i>on</i> the screw by the input force turning it is equal to the work done <i>by</i> the screw on the load force: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle W_{in}=W_{out}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle W_{in}=W_{out}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/a0179c390f6f4c61e5eedefb6def2ebb1d71ffa2" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:12.222ex; height:2.509ex;" alt="{\displaystyle W_{in}=W_{out}\,}"></span></dd></dl> <p>Work is equal to the force multiplied by the distance it acts, so the work done in one complete turn of the screw is <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle W_{in}=2\pi rF_{in}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mo>=</mo> <mn>2</mn> <mi>π</mi> <mi>r</mi> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle W_{in}=2\pi rF_{in}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/023ed00564cb055c3b8f58de989349e643d821dd" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:14.289ex; height:2.509ex;" alt="{\displaystyle W_{in}=2\pi rF_{in}\,}"></span> and the work done on the load is <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle W_{out}=lF_{out}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mi>l</mi> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle W_{out}=lF_{out}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3a3aa6664d2950328a80b0d5146c4a9ed50bd082" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:12.994ex; height:2.509ex;" alt="{\displaystyle W_{out}=lF_{out}\,}"></span>. So the <i>ideal</i> mechanical advantage of a screw is equal to the <i>distance ratio</i>: </p> <div class="equation-box" style="margin: 0 0 0 1.6em;padding: 0px; border-width:1px; border-style: solid; border-color: black; color: inherit;text-align: center; display: table"> <p><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \mathrm {MA} _{ideal}\equiv {\frac {F_{out}}{F_{in}}}={\frac {2\pi r}{l}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mrow class="MJX-TeXAtom-ORD"> <mi mathvariant="normal">M</mi> <mi mathvariant="normal">A</mi> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>d</mi> <mi>e</mi> <mi>a</mi> <mi>l</mi> </mrow> </msub> <mo>≡</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>2</mn> <mi>π</mi> <mi>r</mi> </mrow> <mi>l</mi> </mfrac> </mrow> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \mathrm {MA} _{ideal}\equiv {\frac {F_{out}}{F_{in}}}={\frac {2\pi r}{l}}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c0fccddcfdca01dc1ef8f42709aa4645eb180b88" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.171ex; width:23.517ex; height:5.509ex;" alt="{\displaystyle \mathrm {MA} _{ideal}\equiv {\frac {F_{out}}{F_{in}}}={\frac {2\pi r}{l}}\,}"></span> </p> </div> <p>It can be seen that the mechanical advantage of a screw depends on its lead, <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle l\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>l</mi> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle l\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/db8b3f411aa6977b35e33fffcd39d6713bf4e46b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.338ex; width:1.08ex; height:2.176ex;" alt="{\displaystyle l\,}"></span>. The smaller the distance between its threads, the larger the mechanical advantage, and the larger the force the screw can exert for a given applied force. However most actual screws have large amounts of friction and their mechanical advantage is less than given by the above equation. </p> <div class="mw-heading mw-heading3"><h3 id="Torque_form">Torque form</h3><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=10" title="Edit section: Torque form"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The rotational force applied to the screw is actually a <a href="/wiki/Torque" title="Torque">torque</a> <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle T_{in}=F_{in}r\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>T</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mi>r</mi> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle T_{in}=F_{in}r\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/3dc63bdf20ebc02388d5858bb921b52d723f3d23" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:10.958ex; height:2.509ex;" alt="{\displaystyle T_{in}=F_{in}r\,}"></span>. Because of this, the input force required to turn a screw depends on how far from the shaft it is applied; the farther from the shaft, the less force is needed to turn it. The force on a screw is not usually applied at the rim as assumed above. It is often applied by some form of lever; for example a bolt is turned by a <a href="/wiki/Wrench" title="Wrench">wrench</a> whose handle functions as a lever. The mechanical advantage in this case can be calculated by using the length of the <a href="/wiki/Lever_arm" class="mw-redirect" title="Lever arm">lever arm</a> for <i>r</i> in the above equation. This extraneous factor <i>r</i> can be removed from the above equation by writing it in terms of torque: </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {F_{out}}{T_{in}}}={\frac {2\pi }{l}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>T</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>2</mn> <mi>π</mi> </mrow> <mi>l</mi> </mfrac> </mrow> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {F_{out}}{T_{in}}}={\frac {2\pi }{l}}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d3cc1400adc89d43b899ca3c3bc73f55b904408c" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.171ex; width:11.71ex; height:5.509ex;" alt="{\displaystyle {\frac {F_{out}}{T_{in}}}={\frac {2\pi }{l}}\,}"></span></dd></dl> <div class="mw-heading mw-heading2"><h2 id="Actual_mechanical_advantage_and_efficiency">Actual mechanical advantage and efficiency</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=11" title="Edit section: Actual mechanical advantage and efficiency"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Because of the large area of sliding contact between the moving and stationary threads, screws typically have large frictional energy losses. Even well-lubricated <a href="/wiki/Jack_screw" class="mw-redirect" title="Jack screw">jack screws</a> have <a href="/wiki/Mechanical_efficiency" title="Mechanical efficiency">efficiencies</a> of only 15% - 20%, the rest of the work applied in turning them is lost to friction. When friction is included, the mechanical advantage is no longer equal to the distance ratio but also depends on the screw's efficiency. From <a href="/wiki/Conservation_of_energy" title="Conservation of energy">conservation of energy</a>, the <a href="/wiki/Work_(physics)" title="Work (physics)">work</a> <i>W<sub>in</sub></i> done on the screw by the input force turning it is equal to the sum of the work done moving the load <i>W<sub>out</sub></i>, and the work dissipated as heat by <a href="/wiki/Friction" title="Friction">friction</a> <i>W<sub>fric</sub></i> in the screw </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle W_{in}=W_{out}+W_{fric}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mo>+</mo> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>f</mi> <mi>r</mi> <mi>i</mi> <mi>c</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle W_{in}=W_{out}+W_{fric}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/de3c8d3facab6eceff22fe98aea3a2046cb4ea75" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -1.005ex; width:20.414ex; height:2.843ex;" alt="{\displaystyle W_{in}=W_{out}+W_{fric}\,}"></span></dd></dl> <p>The <a href="/wiki/Mechanical_efficiency" title="Mechanical efficiency">efficiency</a> <i>η</i> is a dimensionless number between 0 and 1 defined as the ratio of output work to input work </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \eta =W_{out}/W_{in}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>η</mi> <mo>=</mo> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \eta =W_{out}/W_{in}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/c2f0fb7be6f00736acc579f82645c779bbeaff33" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:14.554ex; height:2.843ex;" alt="{\displaystyle \eta =W_{out}/W_{in}\,}"></span></dd></dl> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle W_{out}=\eta W_{in}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mi>η</mi> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle W_{out}=\eta W_{in}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d22f6b0535fdf7344c64d279f96b77a1b950eba4" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:13.392ex; height:2.676ex;" alt="{\displaystyle W_{out}=\eta W_{in}\,}"></span></dd></dl> <p><a href="/wiki/Work_(physics)" title="Work (physics)">Work</a> is defined as the force multiplied by the distance moved, so <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle W_{in}=F_{in}d_{in}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle W_{in}=F_{in}d_{in}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/9792252b106c453e6d01bb3a0d43be6df7552840" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:13.74ex; height:2.509ex;" alt="{\displaystyle W_{in}=F_{in}d_{in}\,}"></span> and <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle W_{out}=F_{out}d_{out}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>W</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle W_{out}=F_{out}d_{out}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/417319381ee6dd1240b8e942bf700317fc6ac77b" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.671ex; width:16.073ex; height:2.509ex;" alt="{\displaystyle W_{out}=F_{out}d_{out}\,}"></span> and therefore </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle F_{out}d_{out}=\eta F_{in}d_{in}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mi>η</mi> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle F_{out}d_{out}=\eta F_{in}d_{in}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/7661510c320ee7304a5191e3a7203f7f7564f309" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:18.761ex; height:2.676ex;" alt="{\displaystyle F_{out}d_{out}=\eta F_{in}d_{in}\,}"></span></dd> <dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {F_{out}}{F_{in}}}=\eta {\frac {d_{in}}{d_{out}}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <mi>η</mi> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> </mfrac> </mrow> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {F_{out}}{F_{in}}}=\eta {\frac {d_{in}}{d_{out}}}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/d77e2dd4eee34eb08a670e5128efac9aa7792f74" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.338ex; width:14.158ex; height:5.843ex;" alt="{\displaystyle {\frac {F_{out}}{F_{in}}}=\eta {\frac {d_{in}}{d_{out}}}\,}"></span></dd></dl> <div class="equation-box" style="margin: 0 0 0 1.6em;padding: 0px; border-width:1px; border-style: solid; border-color: black; color: inherit;text-align: center; display: table"> <p><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle MA={\frac {F_{out}}{F_{in}}}=\eta {\frac {2\pi r}{l}}\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>M</mi> <mi>A</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <mi>η</mi> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>2</mn> <mi>π</mi> <mi>r</mi> </mrow> <mi>l</mi> </mfrac> </mrow> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle MA={\frac {F_{out}}{F_{in}}}=\eta {\frac {2\pi r}{l}}\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/40e2cb2b462473e3959d6522988a15b381cba8db" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.171ex; width:21.212ex; height:5.509ex;" alt="{\displaystyle MA={\frac {F_{out}}{F_{in}}}=\eta {\frac {2\pi r}{l}}\,}"></span> </p> </div> <p>or in terms of torque </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle {\frac {F_{out}}{T_{in}}}={\frac {2\pi \eta }{l}}\qquad \,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>T</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> </mfrac> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <mn>2</mn> <mi>π</mi> <mi>η</mi> </mrow> <mi>l</mi> </mfrac> </mrow> <mspace width="2em" /> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle {\frac {F_{out}}{T_{in}}}={\frac {2\pi \eta }{l}}\qquad \,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/2a817598f28490e817c9c3dcb35477f31d7d29d0" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.171ex; width:17.525ex; height:5.676ex;" alt="{\displaystyle {\frac {F_{out}}{T_{in}}}={\frac {2\pi \eta }{l}}\qquad \,}"></span></dd></dl> <p>So the mechanical advantage of an actual screw is reduced from what it would be in an ideal, frictionless screw by the efficiency <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \eta \,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>η</mi> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \eta \,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/41724238aa62aeef8fd437347731c787721cfd04" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:1.557ex; height:2.176ex;" alt="{\displaystyle \eta \,}"></span>. Because of their low efficiency, in powered machinery screws are not often used as linkages to transfer large amounts of power but are more often used in positioners that operate intermittently.<sup id="cite_ref-Bhandari_5-8" class="reference"><a href="#cite_note-Bhandari-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="Self-locking_property">Self-locking property</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=12" title="Edit section: Self-locking property"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Large frictional forces cause most screws in practical use to be "<i>self-locking</i>", also called "<i>non-reciprocal</i>" or "<i>non-overhauling</i>". This means that applying a torque to the shaft will cause it to turn, but no amount of axial load force against the shaft will cause it to turn back the other way, even if the applied torque is zero. This is in contrast to some other <a href="/wiki/Simple_machine" title="Simple machine">simple machines</a> which are "<i>reciprocal</i>" or "<i>non locking</i>" which means if the load force is great enough they will move backwards or "<i>overhaul</i>". Thus, the machine can be used in either direction. For example, in a <a href="/wiki/Lever" title="Lever">lever</a>, if the force on the load end is too large it will move backwards, doing work on the applied force. Most screws are designed to be self-locking, and in the absence of torque on the shaft will stay at whatever position they are left. However, some screw mechanisms with a large enough pitch and good lubrication are not self-locking and will overhaul, and a very few, such as a <a href="/wiki/Drill" title="Drill">push drill</a>, use the screw in this "backwards" sense, applying axial force to the shaft to turn the screw. Other reasons for the screws to come loose are incorrect design of assembly and external forces such as shock, vibration and dynamic loads causing slipping on the threaded and mated/clamped surfaces.<sup id="cite_ref-:0_26-0" class="reference"><a href="#cite_note-:0-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> </p> <figure class="mw-default-size" typeof="mw:File/Thumb"><a href="/wiki/File:Spiral-screwdriver.jpg" class="mw-file-description"><img src="//upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Spiral-screwdriver.jpg/440px-Spiral-screwdriver.jpg" decoding="async" width="440" height="48" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Spiral-screwdriver.jpg/660px-Spiral-screwdriver.jpg 1.5x, //upload.wikimedia.org/wikipedia/commons/thumb/f/f2/Spiral-screwdriver.jpg/880px-Spiral-screwdriver.jpg 2x" data-file-width="1088" data-file-height="118" /></a><figcaption>A <i><a href="/wiki/Screwdriver#Ratcheting_screwdrivers" title="Screwdriver">push drill</a></i>, one of the very few mechanisms that use a screw in the "backwards" sense, to convert linear motion to rotational motion. It has helical screw threads with a very large pitch along the central shaft. When the handle is pushed down, the shaft slides into pawls in the tubular stem, turning the bit. Most screws are "self locking" and axial force on the shaft will not turn the screw.</figcaption></figure> <p>This self-locking property is one reason for the very large use of the screw in <a href="/wiki/Threaded_fastener" class="mw-redirect" title="Threaded fastener">threaded fasteners</a> such as <a href="/wiki/Wood_screw" class="mw-redirect" title="Wood screw">wood screws</a>, <a href="/wiki/Sheet_metal_screw" class="mw-redirect" title="Sheet metal screw">sheet metal screws</a>, studs and bolts. Tightening the fastener by turning it puts compression force on the materials or parts being fastened together, but no amount of force from the parts will cause the screw to turn backwards and untighten. This property is also the basis for the use of screws in <a href="/wiki/Screw_cap" title="Screw cap">screw top container lids</a>, <a href="/wiki/Vise" title="Vise">vises</a>, <a href="/wiki/C-clamp" title="C-clamp">C-clamps</a>, and <a href="/wiki/Screw_jack" class="mw-redirect" title="Screw jack">screw jacks</a>. A heavy object can be raised by turning the jack shaft, but when the shaft is released it will stay at whatever height it is raised to. </p><p>A screw will be self-locking if and only if its efficiency <span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \eta \,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>η</mi> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \eta \,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/41724238aa62aeef8fd437347731c787721cfd04" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -0.838ex; width:1.557ex; height:2.176ex;" alt="{\displaystyle \eta \,}"></span> is below 50%.<sup id="cite_ref-Rao_27-0" class="reference"><a href="#cite_note-Rao-27"><span class="cite-bracket">[</span>27<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Goyal_28-0" class="reference"><a href="#cite_note-Goyal-28"><span class="cite-bracket">[</span>28<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-Gujral2_29-0" class="reference"><a href="#cite_note-Gujral2-29"><span class="cite-bracket">[</span>29<span class="cite-bracket">]</span></a></sup> </p> <dl><dd><span class="mwe-math-element"><span class="mwe-math-mathml-inline mwe-math-mathml-a11y" style="display: none;"><math xmlns="http://www.w3.org/1998/Math/MathML" alttext="{\displaystyle \eta ={\frac {F_{out}/F_{in}}{d_{in}/d_{out}}}={\frac {F_{out}}{F_{in}}}{\frac {l}{2\pi r}}<0.50\,}"> <semantics> <mrow class="MJX-TeXAtom-ORD"> <mstyle displaystyle="true" scriptlevel="0"> <mi>η</mi> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mrow> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> </mrow> <mrow> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> <mrow class="MJX-TeXAtom-ORD"> <mo>/</mo> </mrow> <msub> <mi>d</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> </mrow> </mfrac> </mrow> <mo>=</mo> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>o</mi> <mi>u</mi> <mi>t</mi> </mrow> </msub> <msub> <mi>F</mi> <mrow class="MJX-TeXAtom-ORD"> <mi>i</mi> <mi>n</mi> </mrow> </msub> </mfrac> </mrow> <mrow class="MJX-TeXAtom-ORD"> <mfrac> <mi>l</mi> <mrow> <mn>2</mn> <mi>π</mi> <mi>r</mi> </mrow> </mfrac> </mrow> <mo><</mo> <mn>0.50</mn> <mspace width="thinmathspace" /> </mstyle> </mrow> <annotation encoding="application/x-tex">{\displaystyle \eta ={\frac {F_{out}/F_{in}}{d_{in}/d_{out}}}={\frac {F_{out}}{F_{in}}}{\frac {l}{2\pi r}}<0.50\,}</annotation> </semantics> </math></span><img src="https://wikimedia.org/api/rest_v1/media/math/render/svg/6b631eafa205d2ef941b19774a3f905ed8257271" class="mwe-math-fallback-image-inline mw-invert skin-invert" aria-hidden="true" style="vertical-align: -2.671ex; width:33.597ex; height:6.509ex;" alt="{\displaystyle \eta ={\frac {F_{out}/F_{in}}{d_{in}/d_{out}}}={\frac {F_{out}}{F_{in}}}{\frac {l}{2\pi r}}<0.50\,}"></span></dd></dl> <p>Whether a screw is self-locking ultimately depends on the pitch angle and the <a href="/wiki/Coefficient_of_friction" class="mw-redirect" title="Coefficient of friction">coefficient of friction</a> of the threads; very well-lubricated, low friction threads with a large enough pitch may "overhaul". Also considerations should be made to ensure that clamped components are clamped tight enough to prevent movement completely. If not, slipping in the threads or clamping surface can occur.<sup id="cite_ref-:0_26-1" class="reference"><a href="#cite_note-:0-26"><span class="cite-bracket">[</span>26<span class="cite-bracket">]</span></a></sup> </p> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Screw_mechanism&action=edit&section=13" title="Edit section: References"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r1235681985">.mw-parser-output .side-box{margin:4px 0;box-sizing:border-box;border:1px solid #aaa;font-size:88%;line-height:1.25em;background-color:var(--background-color-interactive-subtle,#f8f9fa);display:flow-root}.mw-parser-output .side-box-abovebelow,.mw-parser-output .side-box-text{padding:0.25em 0.9em}.mw-parser-output .side-box-image{padding:2px 0 2px 0.9em;text-align:center}.mw-parser-output .side-box-imageright{padding:2px 0.9em 2px 0;text-align:center}@media(min-width:500px){.mw-parser-output .side-box-flex{display:flex;align-items:center}.mw-parser-output .side-box-text{flex:1;min-width:0}}@media(min-width:720px){.mw-parser-output .side-box{width:238px}.mw-parser-output .side-box-right{clear:right;float:right;margin-left:1em}.mw-parser-output .side-box-left{margin-right:1em}}</style><style data-mw-deduplicate="TemplateStyles:r1237033735">@media print{body.ns-0 .mw-parser-output .sistersitebox{display:none!important}}@media screen{html.skin-theme-clientpref-night .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .sistersitebox img[src*="Wiktionary-logo-en-v2.svg"]{background-color:white}}</style><div class="side-box side-box-right plainlinks sistersitebox"><style data-mw-deduplicate="TemplateStyles:r1126788409">.mw-parser-output .plainlist ol,.mw-parser-output .plainlist ul{line-height:inherit;list-style:none;margin:0;padding:0}.mw-parser-output .plainlist ol li,.mw-parser-output .plainlist ul li{margin-bottom:0}</style> <div class="side-box-flex"> <div class="side-box-image"><span class="noviewer" typeof="mw:File"><span><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/30px-Commons-logo.svg.png" decoding="async" width="30" height="40" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/45px-Commons-logo.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/4/4a/Commons-logo.svg/59px-Commons-logo.svg.png 2x" data-file-width="1024" data-file-height="1376" /></span></span></div> <div class="side-box-text plainlist">Wikimedia Commons has media related to <span style="font-weight: bold; font-style: italic;"><a href="https://commons.wikimedia.org/wiki/Category:Screw_(simple_machine)" class="extiw" title="commons:Category:Screw (simple machine)">Screw</a></span>.</div></div> </div> <style data-mw-deduplicate="TemplateStyles:r1239543626">.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style><div class="reflist reflist-columns references-column-width" style="column-width: 35em;"> <ol class="references"> <li id="cite_note-Young-1"><span class="mw-cite-backlink">^ <a href="#cite_ref-Young_1-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Young_1-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><style data-mw-deduplicate="TemplateStyles:r1238218222">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free.id-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited.id-lock-limited a,.mw-parser-output .id-lock-registration.id-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription.id-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-free a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-limited a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-registration a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .id-lock-subscription a,body:not(.skin-timeless):not(.skin-minerva) .mw-parser-output .cs1-ws-icon a{background-size:contain;padding:0 1em 0 0}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:var(--color-error,#d33)}.mw-parser-output .cs1-visible-error{color:var(--color-error,#d33)}.mw-parser-output .cs1-maint{display:none;color:#085;margin-left:0.3em}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}@media screen{.mw-parser-output .cs1-format{font-size:95%}html.skin-theme-clientpref-night .mw-parser-output .cs1-maint{color:#18911f}}@media screen and (prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .cs1-maint{color:#18911f}}</style><cite id="CITEREFYoung2000" class="citation web cs1">Young, James F. (2000). <a rel="nofollow" class="external text" href="http://www.clear.rice.edu/elec201/Book/basic_mech.html">"Basic Mechanics"</a>. <i>ELEC 201:Introduction to Engineering Design</i>. Electrical and Computer Engineering Dept., Rice Univ<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-03-29</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=ELEC+201%3AIntroduction+to+Engineering+Design&rft.atitle=Basic+Mechanics&rft.date=2000&rft.aulast=Young&rft.aufirst=James+F.&rft_id=http%3A%2F%2Fwww.clear.rice.edu%2Felec201%2FBook%2Fbasic_mech.html&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMorris1979" class="citation book cs1">Morris, William, Ed. (1979). <a rel="nofollow" class="external text" href="https://archive.org/details/americanheritag00morr/page/1167"><i>The American Heritage Dictionary, New College Edition</i></a>. USA: Houghton Mifflin. pp. <a rel="nofollow" class="external text" href="https://archive.org/details/americanheritag00morr/page/1167">1167</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-395-20360-0" title="Special:BookSources/0-395-20360-0"><bdi>0-395-20360-0</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+American+Heritage+Dictionary%2C+New+College+Edition&rft.place=USA&rft.pages=1167&rft.pub=Houghton+Mifflin&rft.date=1979&rft.isbn=0-395-20360-0&rft.aulast=Morris&rft.aufirst=William%2C+Ed.&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Famericanheritag00morr%2Fpage%2F1167&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span><span class="cs1-maint citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_book" title="Template:Cite book">cite book</a>}}</code>: CS1 maint: multiple names: authors list (<a href="/wiki/Category:CS1_maint:_multiple_names:_authors_list" title="Category:CS1 maint: multiple names: authors list">link</a>)</span></span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://science.howstuffworks.com/screw-info.htm">"Screw"</a>. <i>How Stuff Works website</i>. Discovery Communications. 2011<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-03-29</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=How+Stuff+Works+website&rft.atitle=Screw&rft.date=2011&rft_id=http%3A%2F%2Fscience.howstuffworks.com%2Fscrew-info.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Collins-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-Collins_4-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFCollinsHenry_R._BusbyGeorge_H._Staab2009" class="citation book cs1">Collins, Jack A.; Henry R. Busby; George H. Staab (2009). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=909-5C4eyUkC&q=screw+machine+lead+pitch+advantage&pg=PA464"><i>Mechanical Design of Machine Elements and Machines, 2nd Ed</i></a>. USA: John Wiley and Sons. pp. 462–463. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-470-41303-6" title="Special:BookSources/978-0-470-41303-6"><bdi>978-0-470-41303-6</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Mechanical+Design+of+Machine+Elements+and+Machines%2C+2nd+Ed&rft.place=USA&rft.pages=462-463&rft.pub=John+Wiley+and+Sons&rft.date=2009&rft.isbn=978-0-470-41303-6&rft.aulast=Collins&rft.aufirst=Jack+A.&rft.au=Henry+R.+Busby&rft.au=George+H.+Staab&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D909-5C4eyUkC%26q%3Dscrew%2Bmachine%2Blead%2Bpitch%2Badvantage%26pg%3DPA464&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Bhandari-5"><span class="mw-cite-backlink">^ <a href="#cite_ref-Bhandari_5-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Bhandari_5-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Bhandari_5-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-Bhandari_5-3"><sup><i><b>d</b></i></sup></a> <a href="#cite_ref-Bhandari_5-4"><sup><i><b>e</b></i></sup></a> <a href="#cite_ref-Bhandari_5-5"><sup><i><b>f</b></i></sup></a> <a href="#cite_ref-Bhandari_5-6"><sup><i><b>g</b></i></sup></a> <a href="#cite_ref-Bhandari_5-7"><sup><i><b>h</b></i></sup></a> <a href="#cite_ref-Bhandari_5-8"><sup><i><b>i</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBhandari2007" class="citation book cs1">Bhandari, V. B. (2007). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=d-eNe-VRc1oC&q=%22simple+machine%22+scr&pg=PP12"><i>Design of machine elements</i></a>. New Delhi: Tata McGraw-Hill. pp. 202–206. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-0-07-061141-2" title="Special:BookSources/978-0-07-061141-2"><bdi>978-0-07-061141-2</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Design+of+machine+elements&rft.place=New+Delhi&rft.pages=202-206&rft.pub=Tata+McGraw-Hill&rft.date=2007&rft.isbn=978-0-07-061141-2&rft.aulast=Bhandari&rft.aufirst=V.+B.&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3Dd-eNe-VRc1oC%26q%3D%2522simple%2Bmachine%2522%2Bscr%26pg%3DPP12&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Woods-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-Woods_6-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFWoodsMary_B._Woods2000" class="citation book cs1">Woods, Michael; Mary B. Woods (2000). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=E1tzW_aDnxsC&pg=PA58"><i>Ancient Machines: From Wedges to Waterwheels</i></a>. USA: Twenty-First Century Books. p. 58. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-8225-2994-7" title="Special:BookSources/0-8225-2994-7"><bdi>0-8225-2994-7</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Ancient+Machines%3A+From+Wedges+to+Waterwheels&rft.place=USA&rft.pages=58&rft.pub=Twenty-First+Century+Books&rft.date=2000&rft.isbn=0-8225-2994-7&rft.aulast=Woods&rft.aufirst=Michael&rft.au=Mary+B.+Woods&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DE1tzW_aDnxsC%26pg%3DPA58&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMoorey1999" class="citation book cs1">Moorey, Peter Roger Stuart (1999). <span class="id-lock-limited" title="Free access subject to limited trial, subscription normally required"><a rel="nofollow" class="external text" href="https://archive.org/details/ancientmesopotam00moor"><i>Ancient Mesopotamian Materials and Industries: The Archaeological Evidence</i></a></span>. <a href="/wiki/Eisenbrauns" title="Eisenbrauns">Eisenbrauns</a>. p. <a rel="nofollow" class="external text" href="https://archive.org/details/ancientmesopotam00moor/page/n12">4</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9781575060422" title="Special:BookSources/9781575060422"><bdi>9781575060422</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Ancient+Mesopotamian+Materials+and+Industries%3A+The+Archaeological+Evidence&rft.pages=4&rft.pub=Eisenbrauns&rft.date=1999&rft.isbn=9781575060422&rft.aulast=Moorey&rft.aufirst=Peter+Roger+Stuart&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fancientmesopotam00moor&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Bunch-8"><span class="mw-cite-backlink"><b><a href="#cite_ref-Bunch_8-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBunchAlexander_Hellemans2004" class="citation book cs1">Bunch, Bryan H.; Alexander Hellemans (2004). <span class="id-lock-registration" title="Free registration required"><a rel="nofollow" class="external text" href="https://archive.org/details/isbn_9780618221233"><i>The history of science and technology</i></a></span>. Houghton Mifflin Harcourt. pp. <a rel="nofollow" class="external text" href="https://archive.org/details/isbn_9780618221233/page/69">69</a>. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-618-22123-9" title="Special:BookSources/0-618-22123-9"><bdi>0-618-22123-9</bdi></a>. <q>screw.</q></cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+history+of+science+and+technology&rft.pages=69&rft.pub=Houghton+Mifflin+Harcourt&rft.date=2004&rft.isbn=0-618-22123-9&rft.aulast=Bunch&rft.aufirst=Bryan+H.&rft.au=Alexander+Hellemans&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fisbn_9780618221233&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Krebs-9"><span class="mw-cite-backlink">^ <a href="#cite_ref-Krebs_9-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Krebs_9-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-Krebs_9-2"><sup><i><b>c</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKrebsCarolyn_A._Krebs2003" class="citation book cs1">Krebs, Robert E.; Carolyn A. 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USA: Greenwood Publishing Group. p. 114. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-313-31342-3" title="Special:BookSources/0-313-31342-3"><bdi>0-313-31342-3</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Groundbreaking+scientific+experiments%2C+inventions%2C+and+discoveries+of+the+ancient+world&rft.place=USA&rft.pages=114&rft.pub=Greenwood+Publishing+Group&rft.date=2003&rft.isbn=0-313-31342-3&rft.aulast=Krebs&rft.aufirst=Robert+E.&rft.au=Carolyn+A.+Krebs&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D0H0fjBeseVEC%26q%3Darchimedean%2Bsimple%2Bmachine%26pg%3DPA114&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Britannica-10"><span class="mw-cite-backlink">^ <a href="#cite_ref-Britannica_10-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Britannica_10-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation encyclopaedia cs1"><a rel="nofollow" class="external text" href="http://www.britannica.com/EBchecked/topic/529876/screw">"Screw"</a>. <i>Encyclopædia Britannica online</i>. The Encyclopaedia Britannica Co. 2011<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-03-24</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Screw&rft.btitle=Encyclop%C3%A6dia+Britannica+online&rft.pub=The+Encyclopaedia+Britannica+Co.&rft.date=2011&rft_id=http%3A%2F%2Fwww.britannica.com%2FEBchecked%2Ftopic%2F529876%2Fscrew&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Stewart-11"><span class="mw-cite-backlink"><b><a href="#cite_ref-Stewart_11-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFStewartTerry_A._Howell2003" class="citation book cs1">Stewart, Bobby Alton; Terry A. Howell (2003). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=5cP-81xDWuwC&q=screw+invented+archimedes&pg=PA759"><i>Encyclopedia of water science</i></a>. USA: CRC Press. p. 759. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-8247-0948-9" title="Special:BookSources/0-8247-0948-9"><bdi>0-8247-0948-9</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Encyclopedia+of+water+science&rft.place=USA&rft.pages=759&rft.pub=CRC+Press&rft.date=2003&rft.isbn=0-8247-0948-9&rft.aulast=Stewart&rft.aufirst=Bobby+Alton&rft.au=Terry+A.+Howell&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D5cP-81xDWuwC%26q%3Dscrew%2Binvented%2Barchimedes%26pg%3DPA759&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Haven-12"><span class="mw-cite-backlink">^ <a href="#cite_ref-Haven_12-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-Haven_12-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFHaven2006" class="citation book cs1">Haven, Kendall F. 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USA: Libraries Unlimited. pp. 6–. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/1-59158-264-4" title="Special:BookSources/1-59158-264-4"><bdi>1-59158-264-4</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=One+hundred+greatest+science+inventions+of+all+time&rft.place=USA&rft.pages=6-&rft.pub=Libraries+Unlimited&rft.date=2006&rft.isbn=1-59158-264-4&rft.aulast=Haven&rft.aufirst=Kendall+F.&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D0gBwjLTUzEMC%26q%3Dscrew%2Bhistory%2Binvented%26pg%3DPA7&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-13"><span class="mw-cite-backlink"><b><a href="#cite_ref-13">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFChondros2009" class="citation conference cs1">Chondros, Thomas G. (2009). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=Dkq6_mdW43IC&q=screw+history+invented+archimedes&pg=PA63">"The Development of Machine Design as a Science from Classical Times to Modern Era"</a>. <i>International Symposium on History of Machines and Mechanisms: Proceedings of HMM 2008</i>. USA: Springer. p. 63. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/9781402094859" title="Special:BookSources/9781402094859"><bdi>9781402094859</bdi></a>. 1402094841<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-03-23</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=conference&rft.atitle=The+Development+of+Machine+Design+as+a+Science+from+Classical+Times+to+Modern+Era&rft.btitle=International+Symposium+on+History+of+Machines+and+Mechanisms%3A+Proceedings+of+HMM+2008&rft.place=USA&rft.pages=63&rft.pub=Springer&rft.date=2009&rft.isbn=9781402094859&rft.aulast=Chondros&rft.aufirst=Thomas+G.&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DDkq6_mdW43IC%26q%3Dscrew%2Bhistory%2Binvented%2Barchimedes%26pg%3DPA63&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Kerle-14"><span class="mw-cite-backlink"><b><a href="#cite_ref-Kerle_14-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFKerleKlaus_Mauersberger2010" class="citation conference cs1">Kerle, Hanfried; Klaus Mauersberger (2010). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=65Pz4_XJrgwC&q=screw+invented+archimedes&pg=PA165">"From Archimedean spirals to screw mechanisms - A short historical overview"</a>. <i>The Genius of Archimedes -- 23 Centuries of Influence on Mathematics, Science and Engineering: Proceedings of an International Conference Held at Syracuse, Italy, June 8–10, 2010</i>. Springer. pp. 163–179. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-90-481-9090-4" title="Special:BookSources/978-90-481-9090-4"><bdi>978-90-481-9090-4</bdi></a><span class="reference-accessdate">. Retrieved <span class="nowrap">2011-03-23</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=conference&rft.atitle=From+Archimedean+spirals+to+screw+mechanisms+-+A+short+historical+overview&rft.btitle=The+Genius+of+Archimedes+--+23+Centuries+of+Influence+on+Mathematics%2C+Science+and+Engineering%3A+Proceedings+of+an+International+Conference+Held+at+Syracuse%2C+Italy%2C+June+8%E2%80%9310%2C+2010&rft.pages=163-179&rft.pub=Springer&rft.date=2010&rft.isbn=978-90-481-9090-4&rft.aulast=Kerle&rft.aufirst=Hanfried&rft.au=Klaus+Mauersberger&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D65Pz4_XJrgwC%26q%3Dscrew%2Binvented%2Barchimedes%26pg%3DPA165&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Usher-15"><span class="mw-cite-backlink"><b><a href="#cite_ref-Usher_15-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFUsher1988" class="citation book cs1">Usher, Abbott Payson (1988). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=xuDDqqa8FlwC&q=wedge+and+screw&pg=PA196"><i>A History of Mechanical Inventions</i></a>. USA: Courier Dover Publications. p. 98. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-486-25593-X" title="Special:BookSources/0-486-25593-X"><bdi>0-486-25593-X</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=A+History+of+Mechanical+Inventions&rft.place=USA&rft.pages=98&rft.pub=Courier+Dover+Publications&rft.date=1988&rft.isbn=0-486-25593-X&rft.aulast=Usher&rft.aufirst=Abbott+Payson&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DxuDDqqa8FlwC%26q%3Dwedge%2Band%2Bscrew%26pg%3DPA196&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Laufer1915-16"><span class="mw-cite-backlink"><b><a href="#cite_ref-Laufer1915_16-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFLaufer1915" class="citation journal cs1">Laufer, Berthold (1915). <a rel="nofollow" class="external text" href="https://doi.org/10.1525%2Faa.1915.17.2.02a00220">"The Eskimo Screw as a Culture-Historical Problem"</a>. <i>American Anthropologist</i>. <b>17</b> (2): 396–406. <a href="/wiki/Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<span class="id-lock-free" title="Freely accessible"><a rel="nofollow" class="external text" href="https://doi.org/10.1525%2Faa.1915.17.2.02a00220">10.1525/aa.1915.17.2.02a00220</a></span>. <a href="/wiki/ISSN_(identifier)" class="mw-redirect" title="ISSN (identifier)">ISSN</a> <a rel="nofollow" class="external text" href="https://search.worldcat.org/issn/0002-7294">0002-7294</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=article&rft.jtitle=American+Anthropologist&rft.atitle=The+Eskimo+Screw+as+a+Culture-Historical+Problem&rft.volume=17&rft.issue=2&rft.pages=396-406&rft.date=1915&rft_id=info%3Adoi%2F10.1525%2Faa.1915.17.2.02a00220&rft.issn=0002-7294&rft.aulast=Laufer&rft.aufirst=Berthold&rft_id=https%3A%2F%2Fdoi.org%2F10.1525%252Faa.1915.17.2.02a00220&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-17"><span class="mw-cite-backlink"><b><a href="#cite_ref-17">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://books.google.com/books?id=MlQ7NK9dw7IC&q=screw&pg=PA19">Bunch, Hellemans, 2004, p. 81</a></span> </li> <li id="cite_note-18"><span class="mw-cite-backlink"><b><a href="#cite_ref-18">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="https://books.google.com/books?id=MlQ7NK9dw7IC&q=screw&pg=PA19">Bunch, Hellemans, 2004, p. 80</a></span> </li> <li id="cite_note-Stephen-19"><span class="mw-cite-backlink"><b><a href="#cite_ref-Stephen_19-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFStephenLowell_Cardwell2001" class="citation book cs1">Stephen, Donald; Lowell Cardwell (2001). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=BSfpFLV1nkAC&q=%22simple+machine%22+galileo&pg=PA86"><i>Wheels, clocks, and rockets: a history of technology</i></a>. USA: W. W. Norton & Company. pp. 85–87. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-393-32175-4" title="Special:BookSources/0-393-32175-4"><bdi>0-393-32175-4</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Wheels%2C+clocks%2C+and+rockets%3A+a+history+of+technology&rft.place=USA&rft.pages=85-87&rft.pub=W.+W.+Norton+%26+Company&rft.date=2001&rft.isbn=0-393-32175-4&rft.aulast=Stephen&rft.aufirst=Donald&rft.au=Lowell+Cardwell&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DBSfpFLV1nkAC%26q%3D%2522simple%2Bmachine%2522%2Bgalileo%26pg%3DPA86&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-20"><span class="mw-cite-backlink"><b><a href="#cite_ref-20">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBurnham1915" class="citation book cs1">Burnham, Reuben Wesley (1915). <a rel="nofollow" class="external text" href="https://archive.org/details/mathematicsform01burngoog"><i>Mathematics for Machinists</i></a>. John Wiley & sons, Incorporated. p. <a rel="nofollow" class="external text" href="https://archive.org/details/mathematicsform01burngoog/page/n149">137</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Mathematics+for+Machinists&rft.pages=137&rft.pub=John+Wiley+%26+sons%2C+Incorporated&rft.date=1915&rft.aulast=Burnham&rft.aufirst=Reuben+Wesley&rft_id=https%3A%2F%2Farchive.org%2Fdetails%2Fmathematicsform01burngoog&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-McManus-21"><span class="mw-cite-backlink">^ <a href="#cite_ref-McManus_21-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-McManus_21-1"><sup><i><b>b</b></i></sup></a> <a href="#cite_ref-McManus_21-2"><sup><i><b>c</b></i></sup></a> <a href="#cite_ref-McManus_21-3"><sup><i><b>d</b></i></sup></a> <a href="#cite_ref-McManus_21-4"><sup><i><b>e</b></i></sup></a> <a href="#cite_ref-McManus_21-5"><sup><i><b>f</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFMcManus2004" class="citation book cs1">McManus, Chris (2004). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=20oza63ZuG4C&q=screw+threads+left+right&pg=PA46"><i>Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms and Cultures</i></a>. USA: Harvard University Press. p. 46. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-674-01613-0" title="Special:BookSources/0-674-01613-0"><bdi>0-674-01613-0</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Right+Hand%2C+Left+Hand%3A+The+Origins+of+Asymmetry+in+Brains%2C+Bodies%2C+Atoms+and+Cultures&rft.place=USA&rft.pages=46&rft.pub=Harvard+University+Press&rft.date=2004&rft.isbn=0-674-01613-0&rft.aulast=McManus&rft.aufirst=Chris&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D20oza63ZuG4C%26q%3Dscrew%2Bthreads%2Bleft%2Bright%26pg%3DPA46&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Anderson-22"><span class="mw-cite-backlink"><b><a href="#cite_ref-Anderson_22-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFAnderson1983" class="citation book cs1">Anderson, John G. 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USA: Industrial Press. p. 200. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-8311-1145-3" title="Special:BookSources/0-8311-1145-3"><bdi>0-8311-1145-3</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Technical+shop+mathematics%2C+2nd+Ed.&rft.place=USA&rft.pages=200&rft.pub=Industrial+Press&rft.date=1983&rft.isbn=0-8311-1145-3&rft.aulast=Anderson&rft.aufirst=John+G.&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DBabtEFxgZ2AC%26q%3Dright-handed%2Bleft-handed%2Bscrew%2Bthread%26pg%3DPA200&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-23"><span class="mw-cite-backlink"><b><a href="#cite_ref-23">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFBrown" class="citation web cs1"><a href="/wiki/Sheldon_Brown_(bicycle_mechanic)" title="Sheldon Brown (bicycle mechanic)">Brown, Sheldon</a>. <a rel="nofollow" class="external text" href="http://www.sheldonbrown.com/gloss_p.html#pedal">"Bicycle Glossary: Pedal"</a>. Sheldon Brown<span class="reference-accessdate">. Retrieved <span class="nowrap">2010-10-19</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=unknown&rft.btitle=Bicycle+Glossary%3A+Pedal&rft.pub=Sheldon+Brown&rft.aulast=Brown&rft.aufirst=Sheldon&rft_id=http%3A%2F%2Fwww.sheldonbrown.com%2Fgloss_p.html%23pedal&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Cook-24"><span class="mw-cite-backlink"><b><a href="#cite_ref-Cook_24-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFCook1979" class="citation book cs1">Cook, Theodore Andrea (1979) [1st. Pub. London: Constable and Co: 1914]. <a rel="nofollow" class="external text" href="https://books.google.com/books?id=ea-TStM-07EC&q=%22left-handed%22+screw&pg=PA242"><i>The Curves of Life</i></a>. New York: Dover Publications. p. 242. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/0-486-23701-X" title="Special:BookSources/0-486-23701-X"><bdi>0-486-23701-X</bdi></a>. <a href="/wiki/LCCN_(identifier)" class="mw-redirect" title="LCCN (identifier)">LCCN</a> <a rel="nofollow" class="external text" href="https://lccn.loc.gov/78014678">78014678</a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=The+Curves+of+Life&rft.place=New+York&rft.pages=242&rft.pub=Dover+Publications&rft.date=1979&rft_id=info%3Alccn%2F78014678&rft.isbn=0-486-23701-X&rft.aulast=Cook&rft.aufirst=Theodore+Andrea&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3Dea-TStM-07EC%26q%3D%2522left-handed%2522%2Bscrew%26pg%3DPA242&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Oakley-25"><span class="mw-cite-backlink"><b><a href="#cite_ref-Oakley_25-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFOakley2007" class="citation book cs1">Oakley, Ann (2007). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=-pKgvK0p6skC&q=%22left-handed%22+screw&pg=PA49"><i>Fracture: Adventures of a Broken Body</i></a>. The Policy Press. p. 49. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-1861349378" title="Special:BookSources/978-1861349378"><bdi>978-1861349378</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Fracture%3A+Adventures+of+a+Broken+Body&rft.pages=49&rft.pub=The+Policy+Press&rft.date=2007&rft.isbn=978-1861349378&rft.aulast=Oakley&rft.aufirst=Ann&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3D-pKgvK0p6skC%26q%3D%2522left-handed%2522%2Bscrew%26pg%3DPA49&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-:0-26"><span class="mw-cite-backlink">^ <a href="#cite_ref-:0_26-0"><sup><i><b>a</b></i></sup></a> <a href="#cite_ref-:0_26-1"><sup><i><b>b</b></i></sup></a></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://www.boltscience.com/pages/vibloose.htm">"Self-Loosening of Bolts and Nuts"</a>. <i>www.boltscience.com</i><span class="reference-accessdate">. Retrieved <span class="nowrap">2022-03-10</span></span>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Ajournal&rft.genre=unknown&rft.jtitle=www.boltscience.com&rft.atitle=Self-Loosening+of+Bolts+and+Nuts&rft_id=https%3A%2F%2Fwww.boltscience.com%2Fpages%2Fvibloose.htm&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Rao-27"><span class="mw-cite-backlink"><b><a href="#cite_ref-Rao_27-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFRaoR._Durgaiah2005" class="citation book cs1">Rao, S.; R. Durgaiah (2005). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=vRR4FKAkJl4C&q=%22simple+machine%22+%22&pg=PA80"><i>Engineering Mechanics</i></a>. Universities Press. p. 82. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/81-7371-543-2" title="Special:BookSources/81-7371-543-2"><bdi>81-7371-543-2</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Engineering+Mechanics&rft.pages=82&rft.pub=Universities+Press&rft.date=2005&rft.isbn=81-7371-543-2&rft.aulast=Rao&rft.aufirst=S.&rft.au=R.+Durgaiah&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DvRR4FKAkJl4C%26q%3D%2522simple%2Bmachine%2522%2B%2522%26pg%3DPA80&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Goyal-28"><span class="mw-cite-backlink"><b><a href="#cite_ref-Goyal_28-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGoyalG._S._Raghuvanshi2009" class="citation book cs1">Goyal, M. C.; G. S. Raghuvanshi (2009). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=vRR4FKAkJl4C&pg=PA82"><i>Engineering Mechanics</i></a>. New Delhi: PHI Learning Private Ltd. p. 202. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/978-81-203-3789-3" title="Special:BookSources/978-81-203-3789-3"><bdi>978-81-203-3789-3</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Engineering+Mechanics&rft.place=New+Delhi&rft.pages=202&rft.pub=PHI+Learning+Private+Ltd.&rft.date=2009&rft.isbn=978-81-203-3789-3&rft.aulast=Goyal&rft.aufirst=M.+C.&rft.au=G.+S.+Raghuvanshi&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DvRR4FKAkJl4C%26pg%3DPA82&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> <li id="cite_note-Gujral2-29"><span class="mw-cite-backlink"><b><a href="#cite_ref-Gujral2_29-0">^</a></b></span> <span class="reference-text"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1238218222"><cite id="CITEREFGujral2005" class="citation book cs1">Gujral, I.S. (2005). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=JM0OG-XUyu0C&q=%22simple+machine%22+self-locking&pg=PA382"><i>Engineering Mechanics</i></a>. Firewall Media. p. 382. <a href="/wiki/ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <a href="/wiki/Special:BookSources/81-7008-636-1" title="Special:BookSources/81-7008-636-1"><bdi>81-7008-636-1</bdi></a>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Engineering+Mechanics&rft.pages=382&rft.pub=Firewall+Media&rft.date=2005&rft.isbn=81-7008-636-1&rft.aulast=Gujral&rft.aufirst=I.S.&rft_id=https%3A%2F%2Fbooks.google.com%2Fbooks%3Fid%3DJM0OG-XUyu0C%26q%3D%2522simple%2Bmachine%2522%2Bself-locking%26pg%3DPA382&rfr_id=info%3Asid%2Fen.wikipedia.org%3AScrew+mechanism" class="Z3988"></span></span> </li> </ol></div> <div class="navbox-styles"><style data-mw-deduplicate="TemplateStyles:r1129693374">.mw-parser-output .hlist dl,.mw-parser-output .hlist ol,.mw-parser-output .hlist ul{margin:0;padding:0}.mw-parser-output .hlist dd,.mw-parser-output .hlist dt,.mw-parser-output .hlist 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