Every DIY guide on this site that involves drilling or screwing references the same sizing standard. Bookmark this page: it saves you a trip to the shed to find your caliper.
EU/metric screw sizes are given as M-diameter (mm). UK sizes still use the imperial gauge number. US sizes use a similar # gauge but not identical. Use this table to translate between them.
| Metric (mm) | UK gauge | US gauge | Shank ⌀ | Pilot (softwood) | Pilot (hardwood) | Clearance hole |
|---|---|---|---|---|---|---|
| M2 | #2 | #2 | 2.0 mm | 1.5 mm | 1.7 mm | 2.5 mm |
| M2.5 | #3 | #3 | 2.5 mm | 1.8 mm | 2.0 mm | 3.0 mm |
| M3 | #4 | #4 | 3.0 mm | 2.0 mm | 2.5 mm | 3.5 mm |
| M3.5 | #6 | #6 | 3.5 mm | 2.5 mm | 2.8 mm | 4.0 mm |
| M4 | #8 | #8 | 4.0 mm | 2.8 mm | 3.2 mm | 4.5 mm |
| M4.5 | #9 | #9 | 4.5 mm | 3.0 mm | 3.5 mm | 5.0 mm |
| M5 | #10 | #10 | 5.0 mm | 3.5 mm | 4.0 mm | 5.5 mm |
| M5.5 | #12 | #12 | 5.5 mm | 4.0 mm | 4.5 mm | 6.0 mm |
| M6 | #14 | #14 | 6.0 mm | 4.5 mm | 5.0 mm | 6.5 mm |
| M8 | — | — | 8.0 mm | 6.0 mm | 6.8 mm | 9.0 mm |
| M10 | — | — | 10.0 mm | 7.5 mm | 8.5 mm | 11.0 mm |
For brick, block, plaster or concrete. Colour-coded plastic wall plugs are standard across the EU. Use a masonry drill bit and hammer setting.
| Plug colour | Drill bit (masonry) | Screw size | Hole depth | Typical use |
|---|---|---|---|---|
| Yellow | 5 mm | M3 – M4 | 30 mm | Curtain rails, small hooks, light picture frames |
| Red | 6 mm | M4 – M5 | 35 mm | Shelving brackets, TV mounts (small), coat hooks |
| Brown | 7 mm | M5 – M6 | 40 mm | Large TV mounts, kitchen wall cabinets, radiators |
| Blue | 10 mm | M6 – M8 | 50 mm | Boilers, water heaters, heavy shelving |
| Grey / Green | 14 mm | M10+ | 60 mm | Structural fixings, awnings, gate hinges |