Tap sets are used for putting threading on the inner part of a Metal block. For using a Tap Set, first a Hole has to be drilled on the job using a drill, this hole has to be few mm smaller than the Tap size.
Tap sets consists of 3 type of Taps namely Taper, Plug and Bottoming. For fine pitch Tap sets it is usually set of 2 pcs (Taper and Bottoming).

The Tap Sets are usually made of HSS steel.
And the tapping range available in from 3mm to 150mm.