The chamfer is the name of a part of the tap, the tip of the tap is tepered.

This part cuts the workpiece and processes the screw while cutting or raising it.

In the case of hand taps, #1, #2, and #3 are displayed on the case to indicate the length of the chamfer.

There is no indication of this on the actual product. The length of the chamfer is expressed using the number of threads (pitch) of the screw. 

#1: chamfer length ---- 9 threads 

#2: chamfer length ---- 5P threads

#3: chamfer length ---- 1.5 threads

The specifications of general taps are 2.5 threads for spiral taps and 5 threads for point taps, but there are also other lengths for taps by type and application.
 

Chamfer Length

Length of the chamfer

The length of the chamfer section is required to calculate the tapping depth to ensure the effective thread length.

The length of the chamfer = The pitch of the thread × the number of chamfer  

Distance between metric thread pitches (mm)  --- M10×1.5---1.5(mm)

Pitch of unified threads

The unified thread size is the number of threads between 1 inch is displayed.

The length of one thread (pitch) = 25.4 (mm) ÷ the number of threads

Example: M10×1.5 Tapping of 5 threads with chamfer

Length of chamfer = 1.5×5 = 7.5 (mm)

In particular, for holes with a limit on pilot hole depth, there is a limit to the depth at which the tap can be inserted, so it is necessary to select a tap that takes into account the length with the chamfer.

Through Hole	Blind Hole
A: Chamfer B: Effective thread length C: Chamfer length D: Incomplete thread length

The chamfer is the cutting edge part of the tap, and the longer the chamfer part, the less the load is reduced, but the longer the incomplete threaded part.

If the chamfer is short, the load will be larger, but the incomplete threaded part will be shorter.