Fasteners, in general, are available in metric and imperial diameters and lengths. Often you'll need to convert between the two, or work out alternatives - this guide will help you work out what you need.
| Imperial diameter (inch) | Imperial diameter (inch) | Metric diameter (mm) | Metric Equivalent (primarily for washers) |
|---|---|---|---|
| #1 | 0.073 | 1.854 | |
| #2 | 0.086 | 2.184 | M2 |
| #3 | 0.099 | 2.515 | M2.5 |
| #4 | 0.112 | 2.845 | |
| #5 | 0.125 | 3.175 | M3 |
| #6 | 0.138 | 3.505 | |
| #8 | 0.164 | 4.166 | M4 |
| #10 | 0.190 | 4.826 | |
| #12 | 0.216 | 5.486 | |
| 1/4" | 0.250 | 6.350 | M6 |
| 5/16" | 0.313 | 7.938 | M8 |
| 3/8" | 0.375 | 9.525 | M10 |
| 7/16" | 0.438 | 11.112 | |
| 1/2" | 0.500 | 12.700 | |
| 9/16" | 0.563 | 14.288 | M14 |
| 5/8" | 0.625 | 15.875 | M16 |
| 3/4" | 0.750 | 19.050 | M18 |
| 7/8" | 0.875 | 22.225 | M22 |
| 1" | 1.000 | 25.400 | |
| 1-1/8" | 1.125 | 28.575 | |
| 1-1/4" | 1.250 | 31.750 | |
| 1-3/8" | 1.375 | 34.925 | |
| 1-1/2" | 1.500 | 38.100 | |
| 1-3/4" | 1.750 | 44.450 | |
| 2" | 2.000 | 50.800 | |
| 2-1/4" | 2.250 | 57.150 | |
| 2-1/2" | 2.500 | 63.500 | |
| 2-3/4" | 2.750 | 69.850 | |
| 3" | 3.000 | 76.200 | |
| 3-1/4" | 3.250 | 82.550 | |
| 3-1/2" | 3.500 | 88.900 | |
| 3-3/4" | 3.750 | 95.250 | |
| 4" | 4.000 | 101.600 |