Tapping and Deing

Manual Internal threading operation is called tapping and external threading operation is called deing. Taps and dies are used for thread cutting.

For tapping, a hole equivalent to the minor diameter of the thread is drilled and then tap with the tap set of required size.
For deing, external diameter is finished by machining and then cut the thread with die set of required size.

As a thumb rule, the size of the hole to be drilled for an internal thread is calculated as:

Tap drill size d = D-P

where           D = Size of the thread

                     P = Pitch of the thread

e.g. to find the tap drill size of an M6 thread with 1mm pitch

Tap drill size = 6-1=5mm