Carbon steel taps are used to re-thread damaged and or jammed threads. They may also be used to thread mild steels. Hand Taps come in three styles Taper, Plug or Bottoming. Taper Style: Starts the thread square with the workpiece. Plug Style: Generally used in thru holes. Bottom Style: Generate the thread to the bottom of the hole. A tap set contains 1 taper, 1 plug and 1 bottoming tap.