転造タップのシャンクにpやbとあるが、これは何の表記？ | オーエスジー

The "P" and "B" notations on the forming tap shank represent chamfer length .
In the New Roll Tap (NRT), P (=Plug) is for through hole machining and chamfer length 4P, and B (=Bottoming) is for blind hole machining and is chamfer length 2P.

Since the tap chamfer length remains as an incomplete thread length at the back of the screw after machining, 2P is basically recommended for blind hole machining.
In addition, the longer the chamfer length , the more advantageous the tool life, so we recommend 4P for through hole machining.
However, even if it is a blind hole, if there is enough room in the depth of the pilot hole, it is possible to improve durability by selecting 4P.