Coarse pitch
The default metric thread. When no pitch is written, it’s coarse: an M12 bolt is M12 x 1.75.
Fine pitch
Always written with the pitch, like M12 x 1.5. Some sizes also come in an extra-fine pitch, like M12 x 1.25. Common on automotive and hydraulic parts.
Pitch, not TPI
Metric pitch is the distance from one thread to the next, in millimeters. A bigger number means a coarser thread, the opposite of threads per inch.
1st & 2nd choice
ISO 262 prefers first-choice sizes. Second-choice sizes like M14 and M18 are standard but less common, so check stock before you spec them.
| Size | Diameterinches | Coarsepitch, mm | Finepitch, mm | Extra finepitch, mm |
|---|---|---|---|---|
| M3 | 0.118″ | 0.5mmM3 (M3 x 0.5)≈ 50.8 TPI | 0.35mmM3 x 0.35≈ 72.6 TPI | — |
| M3.52nd choice | 0.138″ | 0.6mmM3.5 (M3.5 x 0.6)≈ 42.3 TPI | 0.35mmM3.5 x 0.35≈ 72.6 TPI | — |
| M4 | 0.157″ | 0.7mmM4 (M4 x 0.7)≈ 36.3 TPI | 0.5mmM4 x 0.5≈ 50.8 TPI | — |
| M5 | 0.197″ | 0.8mmM5 (M5 x 0.8)≈ 31.7 TPI | 0.5mmM5 x 0.5≈ 50.8 TPI | — |
| M6 | 0.236″ | 1mmM6 (M6 x 1)≈ 25.4 TPI | 0.75mmM6 x 0.75≈ 33.9 TPI | — |
| M72nd choice | 0.276″ | 1mmM7 (M7 x 1)≈ 25.4 TPI | 0.75mmM7 x 0.75≈ 33.9 TPI | — |
| M8 | 0.315″ | 1.25mmM8 (M8 x 1.25)≈ 20.3 TPI | 1mmM8 x 1≈ 25.4 TPI | 0.75mmM8 x 0.75≈ 33.9 TPI |
| M10 | 0.394″ | 1.5mmM10 (M10 x 1.5)≈ 16.9 TPI | 1.25mmM10 x 1.25≈ 20.3 TPI | 1mmM10 x 1≈ 25.4 TPI |
| M12 | 0.472″ | 1.75mmM12 (M12 x 1.75)≈ 14.5 TPI | 1.5mmM12 x 1.5≈ 16.9 TPI | 1.25mmM12 x 1.25≈ 20.3 TPI |
| M142nd choice | 0.551″ | 2mmM14 (M14 x 2)≈ 12.7 TPI | 1.5mmM14 x 1.5≈ 16.9 TPI | — |
| M16 | 0.630″ | 2mmM16 (M16 x 2)≈ 12.7 TPI | 1.5mmM16 x 1.5≈ 16.9 TPI | — |
| M182nd choice | 0.709″ | 2.5mmM18 (M18 x 2.5)≈ 10.2 TPI | 1.5mmM18 x 1.5≈ 16.9 TPIalso 2 mm in ISO 262 | — |
| M20 | 0.787″ | 2.5mmM20 (M20 x 2.5)≈ 10.2 TPI | 1.5mmM20 x 1.5≈ 16.9 TPIalso 2 mm in ISO 262 | — |
| M222nd choice | 0.866″ | 2.5mmM22 (M22 x 2.5)≈ 10.2 TPI | 1.5mmM22 x 1.5≈ 16.9 TPIalso 2 mm in ISO 262 | — |
| M24 | 0.945″ | 3mmM24 (M24 x 3)≈ 8.5 TPI | 2mmM24 x 2≈ 12.7 TPI | — |
| M272nd choice | 1.063″ | 3mmM27 (M27 x 3)≈ 8.5 TPI | 2mmM27 x 2≈ 12.7 TPI | — |
| M30 | 1.181″ | 3.5mmM30 (M30 x 3.5)≈ 7.3 TPI | 2mmM30 x 2≈ 12.7 TPI | — |
| M332nd choice | 1.299″ | 3.5mmM33 (M33 x 3.5)≈ 7.3 TPI | 2mmM33 x 2≈ 12.7 TPI | — |
| M36 | 1.417″ | 4mmM36 (M36 x 4)≈ 6.3 TPI | 3mmM36 x 3≈ 8.5 TPI | — |
| M392nd choice | 1.535″ | 4mmM39 (M39 x 4)≈ 6.3 TPI | 3mmM39 x 3≈ 8.5 TPI | — |
| M42 | 1.654″ | 4.5mmM42 (M42 x 4.5)≈ 5.6 TPI | 3mmM42 x 3≈ 8.5 TPI | — |
| M452nd choice | 1.772″ | 4.5mmM45 (M45 x 4.5)≈ 5.6 TPI | 3mmM45 x 3≈ 8.5 TPI | — |
| M48 | 1.890″ | 5mmM48 (M48 x 5)≈ 5.1 TPI | 3mmM48 x 3≈ 8.5 TPI | — |
| M522nd choice | 2.047″ | 5mmM52 (M52 x 5)≈ 5.1 TPI | 4mmM52 x 4≈ 6.3 TPI | — |
| M56 | 2.205″ | 5.5mmM56 (M56 x 5.5)≈ 4.6 TPI | 4mmM56 x 4≈ 6.3 TPI | — |
| M602nd choice | 2.362″ | 5.5mmM60 (M60 x 5.5)≈ 4.6 TPI | 4mmM60 x 4≈ 6.3 TPI | — |
| M64 | 2.520″ | 6mmM64 (M64 x 6)≈ 4.2 TPI | 4mmM64 x 4≈ 6.3 TPI | — |
Where a size has two common fine pitches, the finer one is listed as extra fine (M10 x 1, M12 x 1.25). For M18, M20 and M22 the stocked fine thread is 1.5 mm; ISO 262 also lists a 2 mm fine pitch for those sizes. ISO 261 allows more fine pitches still; this chart sticks to the ones you’ll actually see stocked. Reference information only — verify against the current published standard before use.