M7×1 Tap Drill Size
The number you came for, then the reasoning behind it.
M7×1 tap drill — 75% thread
6 mm
6.026 mm exact · nearest inch drill B (0.2380")
How it's calculated
Tap drill = major diameter − pitch → 7 − 1 = 6 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% | 6.350 mm | 6.4 mm | 0.2500" (E drill) |
| 65% | 6.156 mm | 6.2 mm | 0.2460" (D drill) |
| 75% | 6.026 mm | 6 mm | 0.2380" (B drill) |
| 85% | 5.896 mm | 5.9 mm | 0.2340" (A 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.