Using the rollforming process to make threads has several avantages:

• Chipless tapping
• Stronger threads (formed, and not cut)
• Longer Tap life.

However, the rollformed threads require a larger pre-tap hole diameter than cutting threads.

A properly sized prehole should result in a percentage of 65 to 75%.

                            -- prehole too small --                                                   -- correct prehole --                                            -- prehole too large --    

The next 2 tables will help you to determine the appropriate prehole for your project.

• Prehole table in mm
• Prehole table in inches.