Description

Tap, a screw like tool that has threads like a bolt and two, three, or four longitudinal flutes or grooves and that is used to cut screw threads in a nut or a hole. ... Cut-thread taps are threaded to size before hardening; ground-thread taps are finish-threaded after hardening. Internal threading is done by using a tool called a TAP in a hole drilled to a specific diameter for the thread size and pitch you want to cut. External threads, such as for bolts and studs, are made by using a tool called a DIE, which is applied to a specific diameter of rod for the size and pitch of the threads you want to cut.