Tap

Tap is the cutting tool used to make internal threaded hole. Taps are driven by tap wrenches. Tap for a particular size is available as a set of three taps namely taper tap, intermediate tap and plug tap. 

Taper tap with 6-8 threads tapered is for starting the threading. If it is a through hole, the threading can be completed with only taper tap.

To cut thread in blind holes, other taps are also required to get the maximum possible depth.

Intermediate tap with 4 to 6 threads tapered is used next to taper tap and finally plug tap with 2 to 3 threads tapered is used to finish tapping.