M12×1.75 Tap Drill Size
The number you came for, then the reasoning behind it.
M12×1.75 tap drill — 75% thread
10.2 mm
10.295 mm exact · nearest inch drill Y (0.4040")
How it's calculated
Tap drill = major diameter − pitch → 12 − 1.75 = 10.25 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% | 10.863 mm | 10.9 mm | 0.4219" (27/64 drill) |
| 65% | 10.522 mm | 10.5 mm | 0.4130" (Z drill) |
| 75% | 10.295 mm | 10.2 mm | 0.4040" (Y drill) |
| 85% | 10.068 mm | 10.1 mm | 0.3970" (X 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.