M12 x 1.25 tap drill size
10.8 mm
- Inches
- 0.4252
- Inch bit
- 27/64"
- Thread
- 74%
Drill a 10.8 mm hole before cutting an M12 thread with 1.25 mm pitch. The rule for metric taps is diameter minus pitch.
No metric bits? A 27/64" bit (0.4219 in) gives about 79% thread.
M12 x 1.25 thread and hole sizes
| Thread | M12, 1.25 mm pitch, fine |
|---|---|
| Major diameter | 12 mm 0.4724 in |
| Tap drill | 10.8 mm 0.4252 in |
| Closest inch bit | 27/64" 0.4219 in |
| Clearance hole, close fit | 13 mm |
| Clearance hole, medium fit | 13.5 mm |
Why 10.8 mm
Subtract the pitch from the diameter: 12 minus 1.25 is 10.75 mm, and charts list the nearest stocked bit, 10.8 mm. That leaves 74% 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
- M12 x 1.25 tap
- 10.8 mm drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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