M10×1 Tap Drill Size
The number you came for, then the reasoning behind it.
M10×1 tap drill — 75% thread
9 mm
9.026 mm exact · nearest inch drill T (0.3580")
How it's calculated
Tap drill = major diameter − pitch → 10 − 1 = 9 mm
The exact 75% figure is major − (pitch × 75 / 76.98). The simple subtract-the-pitch rule lands within a hundredth of a millimetre of it, which is why every machinist uses it.
All engagement percentages
| % thread | Exact hole | Metric drill | Inch equivalent |
|---|---|---|---|
| 50% | 9.350 mm | 9.4 mm | 0.3680" (U drill) |
| 65% | 9.156 mm | 9.2 mm | 0.3594" (23/64 drill) |
| 75% | 9.026 mm | 9 mm | 0.3580" (T drill) |
| 85% | 8.896 mm | 8.9 mm | 0.3480" (S drill) |
Which percentage should you actually use?
75% for through-holes in mild steel and aluminium. 65% for blind holes, stainless, titanium and anything where the tap is at risk. 50% for hand-tapping deep holes. The strength you give up going from 75% to 60% is around 5%; the tapping torque you give up is around 30%. In practice the threads almost never fail — the tap does.
75% for through-holes in mild steel and aluminium. 65% for blind holes, stainless, titanium and anything where the tap is at risk. 50% for hand-tapping deep holes. The strength you give up going from 75% to 60% is around 5%; the tapping torque you give up is around 30%. In practice the threads almost never fail — the tap does.