3rd Plug Bottom Tap
The 3rd, plug or bottoming 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 tap; the tapered end ("tap chamfer") of a bottoming tap is too short to successfully start into an un-threaded hole. In the US, they are commonly known as bottoming taps, but in Australia and Britain they are also known as plug taps.
