How does tapping create internal threads in a hole?

Tapping is a machining process used to create internal threads within a hole using a tap, which is a screwlike tool featuring threads similar to a bolt.

The tool is designed with two, three, or four longitudinal flutes or grooves that interrupt the continuity of the threads. This interruption creates sharp cutting edges that remove material as the tool is rotated into the hole. When performed on a machine tool, such as a drill press, a specialized tapping attachment is typically employed. This attachment uses a friction clutch to rotate the tap in the cutting direction; once the desired depth is reached, the mechanism reverses the rotation to back the tap out of the hole.12

Hand taps are categorized by their chamfered threads—taper, plug, and bottoming—to facilitate different stages of thread formation, while machine-specific taps may feature unique geometries, such as long shanks with large-radius bends, to allow for the continuous ejection of finished parts.1