| Thread | Metric bolts and nuts, mm | Hex socket, mm |
||
|---|---|---|---|---|
| standard | reduced | enlarged | ||
| M3 | 5.5 | — | — | — |
| M4 | 7 | — | — | 3 |
| M5 | 8 | — | — | 4 |
| M6 | 10 | — | — | 5 |
| M7 | 11 | — | — | — |
| M8 | 13 | 12 | — | 6 |
| M10 | 17 (16) | 14 | — | 8 |
| M12 | 19 (18) | 17 | 21 (22) | 10 |
| M14 | 22 (21) | 19 | 24 | 12 |
| M16 | 24 | 22 | 27 | 14 |
| M18 | 27 | 24 | 30 | 14 |
| M20 | 30 | 27 | 32 (34) | 17 |
| M22 | 32 (34) | 30 | 36 | 17 |
Note
The across-flats size is the distance between the flats of a bolt head or nut. The standard size is the most common one; reduced and enlarged sizes appear in certain standards and from certain manufacturers. Values in parentheses are legacy or less common sizes. Tightening torques for the same fasteners are in the metric fastener torque table.