M2.5 x 0.45 tap drill size
2.05 mm
- Inches
- 0.0807
- Inch bit
- #46
- Thread
- 77%
Drill a 2.05 mm hole before cutting an M2.5 thread with 0.45 mm pitch. The rule for metric taps is diameter minus pitch.
No metric bits? A #46 bit (0.0810 in) gives about 76% thread.
M2.5 x 0.45 thread and hole sizes
| Thread | M2.5, 0.45 mm pitch, coarse |
|---|---|
| Major diameter | 2.5 mm 0.0984 in |
| Tap drill | 2.05 mm 0.0807 in |
| Closest inch bit | #46 0.0810 in |
| Clearance hole, close fit | 2.7 mm |
| Clearance hole, medium fit | 2.9 mm |
Why 2.05 mm
Subtract the pitch from the diameter: 2.5 minus 0.45 is 2.05 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.
Some charts round this to 2 mm. That cuts a tighter thread (about 86%) and is harder on small taps; 2.05 mm is the standard size.
Tools for this job
- M2.5 x 0.45 tap
- 2.05 mm drill bit
- Tap and drill set
- Drill bit size gauge
- Thread pitch gauge
- Cutting oil for tapping
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