Choice of pre-hole diameter

Tapping by material deformation / rollforming has several advantages when compared with cutting taps:

• Tapping without chips
• More resistant threads
• A better tap life
• Threads with good shiny appearance.

However, rollforming taps demand a precise pre-holes that is usually larger than the one required for a cutting tap.

A correctly-sized pre-hole must achieve a thread fill of 65% to 75%.

Pre-hole too small

Pre-hole correct

Pre-hole too big