A taper tap has several threads ground away at a shallow angle, so it enters and aligns easily but cannot cut near the bottom of a blind hole. A second tap has a shorter lead and does most of the work. A plug — or bottoming — tap is almost square-ended and finishes a blind hole.
A through hole needs only a taper or second tap. A blind hole needs all three in sequence if the thread must run close to the bottom.
The questions welders ask
Do I need all three for every size?
For through holes, no — a second tap alone is enough and is what most people use. The set matters when a fastener must reach the bottom of a blind hole, and that is a design decision made long before the tap comes out of the drawer.
Last reviewed 2026-08-14