M3×0.35 Tap Drill Size
The number you came for, then the reasoning behind it.
M3×0.35 tap drill — 75% thread
2.65 mm
2.659 mm exact · nearest inch drill #37 (0.1040")
How it's calculated
Tap drill = major diameter − pitch → 3 − 0.35 = 2.65 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% | 2.773 mm | 2.8 mm | 0.1100" (#35 drill) |
| 65% | 2.704 mm | 2.7 mm | 0.1065" (#36 drill) |
| 75% | 2.659 mm | 2.65 mm | 0.1040" (#37 drill) |
| 85% | 2.614 mm | 2.6 mm | 0.1015" (#38 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.