Knife breaks which are starting from the tapped holes can occur for various reasons:
1. The tapped hole is dirty and the screws are adjusted too hard
2. Tapped holes in the back might break if the remaining thickness of the material is too thin 
- Not recut after hardening. Make sure of re-cutting. This can be avoided by filling the tapped holes during hardening with some special paste (tapped holes in the back). Also, during knife installation, the worker must be careful.
- Change the design / size of the tapped hole (if possible) or make the back of the knife or the area around the tapped holes soft
