Modern Taps come in many different shapes and sizes, The three main types are Taper ( or First ), Second ( or Plug Tap ) and Bottom ( or third tap), All three have a specific task,
Taper or First tap This small tap is similar to a Second tap but has a more pronounced taper to the cutting edges. This feature gives the taper tap a very gradual cutting action that is less aggressive than that of the plug tap. General use is New threads and cutting threads in soft material.
Second or Intermediate tap This tap has tapered cutting edges, which assist in aligning and starting the tap into an untapped hole. The number of tapered threads typically ranges from 3 to 5. Plug taps are the most commonly used type of tap they are commonly known in Britain as second taps.
Bottoming or Plug tap has a continuous cutting edge with almost no taper — between 1 and 1.5 threads of taper is typical. This feature enables a bottoming tap to cut threads to the bottom of a blind hole. A bottoming tap is usually used to cut threads in a hole that has already been partially threaded using one of the more tapered types of the tap; the tapered end ("tap chamfer") of a bottoming tap is too short to successfully start into an unthreaded hole