M3 x 0.5 tap drill size
2.5 mm
- Inches
- 0.0984
- Inch bit
- #40
- Thread
- 77%
Drill a 2.5 mm hole before cutting an M3 thread with 0.5 mm pitch. The rule for metric taps is diameter minus pitch.
No metric bits? A #40 bit (0.0980 in) gives about 79% thread.
M3 x 0.5 thread and hole sizes
| Thread | M3, 0.5 mm pitch, coarse |
|---|---|
| Major diameter | 3 mm 0.1181 in |
| Tap drill | 2.5 mm 0.0984 in |
| Closest inch bit | #40 0.0980 in |
| Clearance hole, close fit | 3.2 mm |
| Clearance hole, medium fit | 3.4 mm |
Why 2.5 mm
Subtract the pitch from the diameter: 3 minus 0.5 is 2.5 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
- M3 x 0.5 tap
- 2.5 mm drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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