Tap Drill Size Calculator

Inputs

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Standard thread size — sets the major diameter and pitch.
Target percentage of full thread. 75% is the common default; 50–65% taps easier in hard or deep holes.

Results

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Tap drill diameter
5.026mm

M6 at 75% thread.

Use the nearest available drill.

Also computed

Nearest shop drill5mm

5.0 mm common metric drill

Designation shown in the note.

Major diameter6mm

Thread pitch1mm

Minor diameter (100%)4.918mm

Basic internal minor, d − 1.0825·pitch.

Method notes 3 notes
  • % thread is the chart convention: % = 76.98 × (major − tap drill) ÷ pitch. The "major − pitch" rule of thumb gives ≈ 77%.
  • Use the nearest standard drill at or just above this size; going under raises tapping torque and tap breakage sharply for little extra strength.
  • 50–65% thread is plenty in most materials and far easier to tap; reserve 75%+ for thin or soft sections.

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