Screw (simple machine)
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A screw is one of the six simple machines. All screws are helical inclined planes. A screw can convert a rotational force (torque) to a linear force and vice versa. The ratio of threading determines the mechanical advantage of the machine. More threading increases the mechanical advantage. A rough comparison of mechanical advantage can be done by taking the circumference of the shaft of the screw and divide by the distance between the threads.

A screw is a shaft with a helical groove or thread formed on its surface and provision at one end to turn the screw. Its main uses are as a threaded fastener used to hold objects together, and as a simple machine used to translate torque into linear force. It can also be defined as an inclined plane wrapped around a shaft.

Screws come in a variety of shapes and sizes for different purposes.
Thread as found on a screw.


[edit] Examples

* Lead screws and ball screws are specialized screws for translating rotational to linear motion.
* Automated garage doors, where a motor drives a long finely threaded shaft at relatively high speed and lifts the heavy door at a slower rate.
* Archimedes' screw and worm gears are examples of this machine.