Metric sizes are written diameter × pitch in millimeters — an M8×1.25 is 8 mm across with threads 1.25 mm apart. Most sizes have a coarse pitch (the default, written just “M8”) and one or more fine pitches. Cutting your own threads? The tap drill column gives the hole to drill first — in metric it’s simply the diameter minus the pitch.
| Size | Pitch (mm) | Tap drill (mm) |
|---|---|---|
| M3 | 0.50 | 2.5 |
| M4 | 0.70 | 3.3 |
| M5 | 0.80 | 4.2 |
| M6 | 1.00 | 5.0 |
| M8 | 1.25 | 6.8 |
| M10 | 1.50 | 8.5 |
| M12 | 1.75 | 10.2 |
| M14 | 2.00 | 12.0 |
| M16 | 2.00 | 14.0 |
| M18 | 2.50 | 15.5 |
| M20 | 2.50 | 17.5 |
| M22 | 2.50 | 19.5 |
| M24 | 3.00 | 21.0 |
Metric and inch don’t mix. Some sizes look alike — an M8 is almost a 5/16″ — but they won’t actually thread together. If you’re not sure which system you have, see metric vs. inch. Working in inch sizes instead? Here’s the inch thread pitch & tap-drill chart.
Not sure of a pitch? Bring the bolt to either counter and we’ll gauge it — an instant, exact read.
