description
A screw is a combination of simple machines—it is, in essence, an inclined plane wrapped around a central shaft, but the inclined plane (thread) also comes to a sharp edge around the outside, which acts a wedge as it pushes into the fastened material, and the shaft and helix also form a wedge in the form of the point. Some screw threads are designed to mate with a complementary thread, known as a female thread (internal thread), often in the form of a nut, or object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted. The most common uses of screws are to hold objects together and to position objects.