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M8 x 1 tap drill size
Use a 7 mm drill to tap M8 x 1 (fine pitch). The rule is major diameter minus pitch: 8 − 1 = 7 mm. Closest inch drill: J (7.04 mm).
M8 x 1 thread specifications
| Thread | M8 x 1 ISO metric fine |
|---|---|
| Major (nominal) diameter | .3150 in / 8.00 mm |
| Pitch | 1 mm (≈ 25.4 threads per inch) |
| Recommended tap drill | 7 mm = .2756 in |
M8 clearance hole (ISO 273)
| Fit | Hole diameter |
|---|---|
| Fine (close) | 8.4 mm |
| Medium (normal) | 9 mm |
| Coarse (loose) | 10 mm |
A clearance hole lets the M8 bolt pass through freely. Drill the tap-drill size only in the part that gets threaded.
Tips for tapping M8 x 1
- 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 (4.0 mm here).
- Thread engagement of 1–1.5 × the diameter (8.0–12.0 mm) is enough for most steel parts. Softer materials need more.