Screw mechanism

The screw is a mechanism that converts <a href="/facts/Rotation/yChkz49x">rotational</a> motion to <a href="/facts/Linear_motion/Vom0QwWe">linear motion</a>, and a <a href="/facts/Torque/KcrcvNtV">torque</a> (rotational force) to a linear <a href="/facts/Force/533Q1uzq">force</a>. It is one of the six classical <a href="/facts/Simple_machine/Elcq1eXY">simple machines</a>. The most common form consists of a cylindrical shaft with <a href="/facts/Helix/BqC4AKwL">helical</a> grooves or ridges called <a href="/facts/Screw_thread/dqGzDfHv">threads</a> around the outside. 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="/facts/Wood_screw/Rr0k38TC">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="/facts/Nut_(hardware)/RvmcvYH8">nut</a> can rotate around a stationary screw shaft. Geometrically, a screw can be viewed as a narrow <a href="/facts/Inclined_plane/h7XSGAcR">inclined plane</a> wrapped around a <a href="/facts/Cylinder_(geometry)/0wQPPr3k">cylinder</a>.
Like the other simple machines a screw can amplify force; a small rotational force (<a href="/facts/Torque/KcrcvNtV">torque</a>) on the shaft can exert a large axial force on a load. The smaller the <a href="/facts/Pitch_(screw)/dqGzDfHv">pitch</a> (the distance between the screw's threads), the greater the <a href="/facts/Mechanical_advantage/tWX3c82Q">mechanical advantage</a> (the ratio of output to input force). Screws are widely used in <a href="/facts/Threaded_fastener/earBwoS6">threaded fasteners</a> to hold objects together, and in devices such as <a href="/facts/Screw_top/XKPF3tDK">screw tops</a> for containers, <a href="/facts/Vise/JWJRfIkA">vises</a>, <a href="/facts/Screw_jack/B9kjdeBt">screw jacks</a> and <a href="/facts/Screw_press/13ULaoUl">screw presses</a>.
Other mechanisms that use the same principle, also called screws, do not necessarily have a shaft or threads. For example, a <a href="/facts/Corkscrew/mv1jpFLb">corkscrew</a> is a helix-shaped rod with a sharp point, and an <a href="/facts/Archimedes%27_screw/MmkM1w4y">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="/facts/Helix/BqC4AKwL">helix</a> can cause linear motion.

Screw mechanism open-in-new

Screw mechanism