Nut tap -What is a nut tap?
Today there is a short Wiki about the nut tap:
What a nut tap and when is it used?
Nut taps are used to produce nuts with metric ISO standard threads according to DIN 13-1. Nut taps have a very long lead ( 2/3 of the thread length) and are suitable for thread depths up to 1.5 x nominal diameter in short through holes. The purpose of the nut taps with 2/3 lead is durability (long service life) due to good cutting distribution. The surface of the cut thread is also very smooth, which is very important for nuts that have to be loosened frequently. The construction dimensions are regulated in the DIN standard 357 (for metric iso-thread from M3 to M 68).