What is a screw primarily considered to be in mechanical terms?

A screw is primarily considered a simple machine that converts rotational motion into linear motion. When the screw is turned, the rotational force applied to the head causes the threaded shaft to move linearly, either into or out of a material. This mechanical advantage allows a relatively small rotational force to produce significant linear force, which can be utilized effectively in various applications, such as fastening objects together or lifting loads. The helical structure of the screw thread facilitates this conversion, making it a fundamental tool in mechanics and engineering.