Hand taps and die are used to create screw threads ,which is called threading . Both tap and die can be used to either cut new threads or repair damaged threads. Threading is divided into two types, internal and external.
Internal threading – 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. Moreover , applied to a specific diameter of rod for the size and pitch of the threads you want to cut.
Taps and dies come in various configurations and materials, the most common being High Speed Steel (HSS) for softer materials as well as Cobalt for hard materials like stainless.