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M3 x 0.5 tap drill size
Use a 2.5 mm drill to tap M3 x 0.5 (coarse pitch). The rule is major diameter minus pitch: 3 − 0.5 = 2.5 mm. Closest inch drill: #40 (2.49 mm).
M3 x 0.5 thread specifications
| Thread | M3 x 0.5 ISO metric coarse |
|---|---|
| Major (nominal) diameter | .1181 in / 3.00 mm |
| Pitch | 0.5 mm (≈ 50.8 threads per inch) |
| Recommended tap drill | 2.5 mm = .0984 in |
M3 clearance hole (ISO 273)
| Fit | Hole diameter |
|---|---|
| Fine (close) | 3.2 mm |
| Medium (normal) | 3.4 mm |
| Coarse (loose) | 3.6 mm |
A clearance hole lets the M3 bolt pass through freely. Drill the tap-drill size only in the part that gets threaded.
Tips for tapping M3 x 0.5
- Use cutting fluid, and with a hand tap back off about half a turn every turn or two to break the chip. Aluminium and soft materials are the exception: they tap cleanly with spiral-point taps.
- For blind holes, drill deeper than the thread you need. Allow at least 3–4 pitches beyond the last full thread for a plug tap (2.0 mm here).
- Thread engagement of 1–1.5 × the diameter (3.0–4.5 mm) is enough for most steel parts. Softer materials need more.