Serial Tap sets (designated as
Rougher, Intermediate and Finisher) actually vary in thread diameter, unlike conventional tap sets (
Taper, Second and Plug) where the difference between each one is the length of the taper.
Because the major and pitch diameter of the
Rougher is smaller than the
Intermediate, and the
Intermediate is smaller than the
Finisher, each tap removes a smaller volume of metal resulting in a extremely smooth thread.
Excellent for tapping deep holes and tough metals such as stainless steel.