Tap drill size is major diameter minus pitch

For a metric thread, the drill bit for tapping is simply the major diameter minus the thread pitch — M6×1.0 needs a 5.0mm hole, no lookup table required.

Why it works

This targets roughly 75% thread engagement, the standard compromise between thread strength and how much force it takes to actually cut the tap through the material — 100% engagement is dramatically harder to tap for very little extra holding strength.

Do it exactly

Estimate with the rule, then check it against the calculator that models it properly.

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