Tools reference
Clearance hole size chart: close, normal, and free fits
ISO 273 clearance-hole sizes for common metric bolts, with a clear separation between close, normal, free, and tap-drill holes.
Reviewed against GaugeFox data and the sources below · Updated August 29, 2026
Common metric clearance-hole sizes
| Bolt thread | Close | Normal | Free |
|---|---|---|---|
| M3 | 3.2 mm | 3.4 mm | 3.6 mm |
| M4 | 4.3 mm | 4.5 mm | 4.8 mm |
| M5 | 5.3 mm | 5.5 mm | 5.8 mm |
| M6 | 6.4 mm | 6.6 mm | 7.0 mm |
| M8 | 8.4 mm | 9.0 mm | 10.0 mm |
| M10 | 10.5 mm | 11.0 mm | 12.0 mm |
| M12 | 13.0 mm | 13.5 mm | 14.5 mm |
How to choose among the three fits
- Close: use when location matters and the parts, drilling, and alignment are controlled.
- Normal: a practical general-purpose choice for ordinary assembly.
- Free: useful when easy assembly, field tolerance, or misalignment matters more than close location.
Do not replace the tap drill with this number
The clearance sizes above are all larger than the named bolt diameter. A tap drill must be smaller so the tap still has material to cut. GaugeFox keeps the two results in separate labeled sections for that reason.
The table covers verified ISO 273 metric entries. GaugeFox does not manufacture an inch-series clearance answer from a metric table when an independently reviewed source is not attached to that record.
Reference trail
Sources and review method
These source pages identify the standards or industry references used for this guide. Full standards may require purchase. The guide is an identification aid, not a substitute for a calibrated inspection or the complete applicable standard.
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