A screw is a fastener, sometimes similar to a bolt, usually made of metal, characterized by a spiral ridge, called an external thread (external thread) or a positive thread.

A screw is an inclined plane wound around a nail. Some threads are designed to mate with complementary threads called female threads (internal threads) in the form of objects commonly known as nuts or with internal threads. Other threads are designed to cut a spiral groove in the softer material when the screw is inserted. The most common use of screws is to hold objects together and place them.

A screw usually has a head at one end, which has a specially formed shape that allows the screw to be rotated or driven using a tool. Common tools for driving screws include screwdriver and wrench. The head is usually larger than the body of the screw, which prevents the screw from being driven deeper than the length of the screw and provides a bearing surface. There are exceptions; for example, the dome head of a pulley bolt cannot be driven. The head of the set screw is usually smaller than the outside diameter of the screw; the J-bolt has a j-head, which is not designed for driving, but usually sinks into the concrete to be used as the anchor bolt. The cylindrical part of the screw from the lower side of the head to the tip is called the shank. It can be full thread or partial thread. The distance between each thread is called "pitch.".

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