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Tap drill and clearance hole sizes (metric)

Tap drill and ISO clearance hole for metric threads.

mm

Calculating…

How it's calculated

Tap drill ≈ major diameter − pitch (≈75% thread)

Major diameter minus pitch gives roughly 75% thread engagement, the normal choice for cutting taps. Form (roll) taps need a larger hole; use the tap maker's chart. Clearance holes are from ISO 273: close, medium and free (coarse) fits.