Tap (tool)

A tap is a tool, usually of very hard metal, which is used to cut threads into the sides of a predrilled hole. These threads accepts a threaded fastener such as a machine screw or bolt (fastener).

Tapping can be done by hand or motor power. In general, a machine, such as a drill press, is preferable in order to keep the tap in perfect vertical alignment with the hole, and to maintain a steady level of pressure. Besides the problem of making irregular threads, an out-of-alignment tap can break the tap, which is made from hard but brittle material.

The most common means of hand-powering a tap is by use of a tap wrench, which has an adjustable set of jaws for holding the tap, and a T-shaped handle for turning the wrench-tap assembly. Taps usually have a square head that is gripped by the jaws.