imageTAPER
8 to 10 threads chamfered for easy thread starting in rough materials.

imagePLUG
3 to 5 threads chamfered - general use when tapping to bottom of holes is not critical. (This is the most widely used type of tap.)

imageBOTTOMING
1-1/2 threads chamfered - use after threads have been started for tapping to bottom of hole.