M8 x 1 tap drill size
7 mm
- Inches
- 0.2756
- Inch bit
- Letter J
- Thread
- 77%
Drill a 7 mm hole before cutting an M8 thread with 1 mm pitch. The rule for metric taps is diameter minus pitch.
No metric bits? A Letter J bit (0.2770 in) gives about 74% thread.
M8 x 1 thread and hole sizes
| Thread | M8, 1 mm pitch, fine |
|---|---|
| Major diameter | 8 mm 0.3150 in |
| Tap drill | 7 mm 0.2756 in |
| Closest inch bit | Letter J 0.2770 in |
| Clearance hole, close fit | 8.4 mm |
| Clearance hole, medium fit | 9 mm |
Why 7 mm
Subtract the pitch from the diameter: 8 minus 1 is 7 mm. That leaves 77% thread, the usual target for a cut tap.
More thread than that adds almost no strength and makes the tap much easier to break. In hard or tough material, go 0.1 mm larger.
Tools for this job
- M8 x 1 tap
- 7 mm drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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