Screw

A screw is a cylindrical fastener made of coated steel or non-ferrous alloy. One end of the cylinder has external thread cut into it, while the other has a feature for driving the screw into the part being fastened.

This feature is most often a head of various designs, and sometimes a recess on the end face. A screw joint does not require a nut or reinforcement such as adhesive or mortar. Depending on the application, screws of the following designs are used:

• with round, countersunk, raised countersunk, or flat head;
• with cylindrical end;
• with hex socket;
• with enlarged/reduced head and slot;
• headless, with dog point and slot.