M18 × 1.5 tap drill size
16.50 mm drill — or 21/32 (0.6563 in) = 68% thread
M18 fine series, 1.5 mm pitch. Tap drill Ø = nominal − pitch = 18 − 1.5 = 16.50 mm (≈77% thread, the standard chart value).
| Drill | Size | Thread % |
|---|---|---|
| 16.50 mm | 0.6496 in | 77% |
| 21/32 (inch) | 0.6563 in / 16.67 mm | 68% |
Rounding to your nearest stock drill moves the thread percentage only a few points. Cut taps only — roll-form taps need a larger hole. Verify before you cut.
Need a different thread percentage? Open the tap drill calculator · Metric tap chart · All calculators