special screw(bolt)

special screw(bolt)
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.
Mechanical advantage
The mechanical advantage of a screw without using a screwdriver is:

P = Pitch of screw (The distance between two adjacent screw threads is called the pitch.)
C = Circumference of the shank of the screw.
MA = C / P.

The same formula can be used when using a screwdriver, but with:

C = Circumference of the screwdriver handle.