Metric screw size chart
An M6 screw is 6.0 mm across with a 1.0 mm coarse pitch and a 5.00 mm tap drill.
Metric tap drills here follow the rule of diameter minus pitch. Clearance holes follow ISO 273; the table shows the medium fit and the drill finder gives all three. Add a pitch in the lookup, for example M8 x 1, to get the fine thread.
| Size | Diameter (mm) | Coarse pitch | Tap drill | Fine pitches | Clearance (medium) |
|---|---|---|---|---|---|
| M1.6 | 1.6 | 0.35 mm | 1.25 mm | - | 1.8 mm |
| M2 | 2.0 | 0.4 mm | 1.60 mm | - | 2.4 mm |
| M2.5 | 2.5 | 0.45 mm | 2.05 mm | - | 2.9 mm |
| M3 | 3.0 | 0.5 mm | 2.50 mm | - | 3.4 mm |
| M3.5 | 3.5 | 0.6 mm | 2.90 mm | - | 3.9 mm |
| M4 | 4.0 | 0.7 mm | 3.30 mm | 0.5 mm (tap 3.50) | 4.5 mm |
| M5 | 5.0 | 0.8 mm | 4.20 mm | 0.5 mm (tap 4.50) | 5.5 mm |
| M6 | 6.0 | 1.0 mm | 5.00 mm | 0.75 mm (tap 5.25) | 6.6 mm |
| M8 | 8.0 | 1.25 mm | 6.80 mm | 1.0 mm (tap 7.00) | 9.0 mm |
| M10 | 10.0 | 1.5 mm | 8.50 mm | 1.25 mm (tap 8.75), 1.0 mm (tap 9.00) | 11.0 mm |
| M12 | 12.0 | 1.75 mm | 10.20 mm | 1.5 mm (tap 10.50), 1.25 mm (tap 10.75) | 13.5 mm |
| M14 | 14.0 | 2.0 mm | 12.00 mm | 1.5 mm (tap 12.50) | 15.5 mm |
| M16 | 16.0 | 2.0 mm | 14.00 mm | 1.5 mm (tap 14.50) | 17.5 mm |
| M18 | 18.0 | 2.5 mm | 15.50 mm | 2.0 mm (tap 16.00), 1.5 mm (tap 16.50) | 20.0 mm |
| M20 | 20.0 | 2.5 mm | 17.50 mm | 2.0 mm (tap 18.00), 1.5 mm (tap 18.50) | 22.0 mm |
| M22 | 22.0 | 2.5 mm | 19.50 mm | 2.0 mm (tap 20.00), 1.5 mm (tap 20.50) | 24.0 mm |
| M24 | 24.0 | 3.0 mm | 21.00 mm | 2.0 mm (tap 22.00) | 26.0 mm |
How to read a metric size
M6 means a 6 mm nominal diameter. M6 x 1 adds the pitch, the distance between threads, in millimetres. When no pitch is written the coarse pitch is assumed: 1 mm for M6, 1.25 mm for M8. Fine pitches exist for most sizes and are always written out, for example M8 x 1.
Tap drill and clearance hole
For a standard 60 degree thread the tap drill is the diameter minus the pitch, so M6 takes a 5 mm drill. Clearance holes follow ISO 273 in three classes. Fine suits accurate positioning, medium is the usual choice, and coarse tolerates more misalignment between parts. For M6 the three are 6.4, 6.6 and 7 mm.
Metric versus inch
The two systems are close but not interchangeable. M6 is 6 mm across and 1/4 inch is 6.35 mm, and the pitches differ, so a metric screw in an inch thread will bind or strip. Check the label before you drill.