A screw thread is a form of simple machine. A simple screw consists of a rod, which has a thread. The distance between two threads is called the Pitch and the handle of the screw is called the Effort. It is the point of rotation at which effort is applied.
For screws to operate, when the effort moves a complete circumference of the circle, the load moves a corresponding distance.
Screws come in varying shapes, depending on their intended use and the tools used to install them. Screws used to anchor wood, called wood screws, generally have pointed tips.
Uses of screw thread are:
1. For fixing wood to wood or wood to metal.
2. Used in making holes in hard materials such as wood and soft iron.
3. For fixing mirrors.
4. For fixing fittings to metal window frames.
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