Clearance Hole Sizes
Clearance (through-hole) sizes for inch and metric bolts in close, normal and loose fit — the hole the bolt passes through, per ASME B18.2.8 and ISO 273.
Unified (inch)
| Bolt size | Close H12 · ″ | Normal H13 · ″ | Loose H14 · ″ |
|---|---|---|---|
| #4 | 0.12 | 0.128 | 0.144 |
| #6 | 0.154 | 0.17 | 0.185 |
| #8 | 0.18 | 0.196 | 0.213 |
| #10 | 0.206 | 0.221 | 0.238 |
| 1/4 | 0.266 | 0.281 | 0.297 |
| 5/16 | 0.328 | 0.344 | 0.359 |
| 3/8 | 0.391 | 0.406 | 0.422 |
| 7/16 | 0.453 | 0.469 | 0.484 |
| 1/2 | 0.531 | 0.562 | 0.609 |
| 5/8 | 0.656 | 0.688 | 0.734 |
| 3/4 | 0.781 | 0.812 | 0.906 |
| 7/8 | 0.906 | 0.938 | 1.031 |
| 1 | 1.031 | 1.094 | 1.156 |
Metric
| Bolt size | Close H12 · mm | Normal H13 · mm | Loose H14 · mm |
|---|---|---|---|
| M3 | 3.2 | 3.4 | 3.6 |
| M4 | 4.3 | 4.5 | 4.8 |
| M5 | 5.3 | 5.5 | 5.8 |
| M6 | 6.4 | 6.6 | 7 |
| M8 | 8.4 | 9 | 10 |
| M10 | 10.5 | 11 | 12 |
| M12 | 13 | 13.5 | 14.5 |
| M14 | 15 | 15.5 | 16.5 |
| M16 | 17 | 17.5 | 18.5 |
| M18 | 19 | 20 | 21 |
| M20 | 21 | 22 | 24 |
| M22 | 23 | 24 | 26 |
| M24 | 25 | 26 | 28 |
| M27 | 28 | 30 | 32 |
| M30 | 31 | 33 | 35 |
Clearance hole vs. tap drill — don't mix them up. The clearance hole is the plain through-hole on the part the bolt passes through; the tap drill is the smaller hole you thread on the part the bolt screws into. Drilling a tap-drill-sized hole where you need clearance will bind the bolt.
One page per size
Each size has its own page with both units, the tolerance band, the threads that share that nominal, and a calculator.