Tap Drill Size Calculator

Determine the correct drill bit size required before tapping a hole for internal threads (Metric and Imperial).

Parameters

Thread Standard

Major Diameter (mm)

Thread Pitch (mm)

Required Drill Bit Size

8.500 mm

Engineering Formula Used

Drill Size (mm) = Major Diameter (mm) - Pitch (mm)

Note: This calculates the theoretical 100% thread engagement drill size. For practical applications, machinists often use a slightly larger drill bit (for 75% thread engagement) to prevent tap breakage.