M22×1.5 Tap Drill Size
The number you came for, then the reasoning behind it.
M22×1.5 tap drill — 75% thread
20.5 mm
20.539 mm exact · nearest inch drill 13/16 (0.8125")
How it's calculated
Tap drill = major diameter − pitch → 22 − 1.5 = 20.5 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% | 21.026 mm | 21 mm | 0.8281" (53/64 drill) |
| 65% | 20.733 mm | 20.7 mm | 0.8125" (13/16 drill) |
| 75% | 20.539 mm | 20.5 mm | 0.8125" (13/16 drill) |
| 85% | 20.344 mm | 20.3 mm | 0.7969" (51/64 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.