Thread pitches, spanner sizes and Allen key sizes for metric and inch fasteners — plus inch-to-mm conversion and SWG wire gauges. A quick reference for the counter, the workshop and the site.
Metric (ISO) fasteners. Coarse pitch is the standard thread unless fine is asked for. Where two spanner sizes are shown (e.g. 16 / 17), the first is the newer ISO size and the second the older DIN size.
| Size | Thread Pitch (mm) | Spanner (mm) | Allen Key (mm) | ||||
|---|---|---|---|---|---|---|---|
| Coarse Standard | Fine | Hex Head A/F ISO / DIN |
Socket Cap | Allen CSK | Grub Screw | Button Head | |
| M1 | 0.25 | — | — | — | — | — | — |
| M1.6 | 0.35 | — | 3.2 | 1.5 | — | — | — |
| M2 | 0.4 | — | 4 | 1.5 | — | — | — |
| M2.5 | 0.45 | — | 5 | 2 | — | — | — |
| M3 | 0.5 | — | 5.5 | 2.5 | 2 | 1.5 | 2 |
| M3.5 | 0.6 | — | 6 | — | — | — | — |
| M4 | 0.7 | — | 7 | 3 | 2.5 | 2 | 2.5 |
| M5 | 0.8 | — | 8 | 4 | 3 | 2.5 | 3 |
| M6 | 1 | — | 10 | 5 | 4 | 3 | 4 |
| M8 | 1.25 | 1 | 13 | 6 | 5 | 4 | 5 |
| M10 | 1.5 | 1.25 / 1 | 16 / 17 | 8 | 6 | 5 | 6 |
| M12 | 1.75 | 1.5 / 1.25 | 18 / 19 | 10 | 8 | 6 | 8 |
| M14 | 2 | 1.5 | 21 / 22 | 12 | 10 | 6 | — |
| M16 | 2 | 1.5 | 24 | 14 | 10 | 8 | — |
| M18 | 2.5 | 2 / 1.5 | 27 | 14 | 12 | 10 | — |
| M20 | 2.5 | 2 / 1.5 | 30 | 17 | 12 | 10 | — |
| M22 | 2.5 | 2 / 1.5 | 32 | 17 | 14 | 12 | — |
| M24 | 3 | 2 | 36 | 19 | 14 | 12 | — |
| M27 | 3 | 2 | 41 | 19 | — | — | — |
| M30 | 3.5 | 2 | 46 | 22 | — | — | — |
| M33 | 3.5 | 2 | 50 | 24 | — | — | — |
| M36 | 4 | 3 | 55 | 27 | — | — | — |
| M39 | 4 | 3 | 60 | — | — | — | — |
| M42 | 4.5 | 3 | 65 | 32 | — | — | — |
| M45 | 4.5 | 3 | 70 | — | — | — | — |
| M48 | 5 | 3 | 75 | — | — | — | — |
| M52 | 5 | 4 | 80 | — | — | — | — |
| M56 | 5.5 | 4 | 85 | — | — | — | — |
| M60 | 5.5 | 4 | 90 | — | — | — | — |
| M64 | 6 | 4 | 95 | — | — | — | — |
| M68 | — | — | 100 | — | — | — | — |
| M72 | — | — | 105 | — | — | — | — |
Inch fasteners. Thread counts are in threads per inch (TPI): BSW British Standard Whitworth, BSF British Standard Fine, UNC Unified Coarse, UNF Unified Fine. Spanner sizes are marked in mm or inches.
| Size | = mm | Threads per Inch (TPI) | Spanner | Allen Key | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
| BSW | BSF | UNC | UNF | Hex Head A/F | Socket Cap | Allen CSK | Grub Screw | Button Head | ||
| 1/8" | 3.175 | 40 | — | — | — | — | 3/32" | 1/16" | 1/16" | — |
| 5/32" | 3.969 | — | — | — | — | — | 1/8" | — | — | — |
| 3/16" | 4.762 | 24 | 32 | — | — | 8 mm | 5/32" | 3/32" | 3/32" | 1/8" |
| 1/4" | 6.350 | 20 | 26 | 20 | 28 | 11 mm | 3/16" | 5/32" | 1/8" | 5/32" |
| 5/16" | 7.938 | 18 | 22 | 18 | 24 | 13 mm | 7/32" | 3/16" | 5/32" | 3/16" |
| 3/8" | 9.525 | 16 | 20 | 16 | 24 | 15 mm | 5/16" | 7/32" | 3/16" | 7/32" |
| 7/16" | 11.112 | 14 | 18 | 14 | 20 | 17 mm | 5/16" | 1/4" | 7/32" | 1/4" |
| 1/2" | 12.700 | 12 | 16 | 13 | 20 | 20 mm | 3/8" | 5/16" | 1/4" | 5/16" |
| 9/16" | 14.287 | 12 | 16 | 12 | 18 | 7/8" | 3/8" | 5/16" | 1/4" | — |
| 5/8" | 15.875 | 11 | 14 | 11 | 18 | 1" | 1/2" | 3/8" | 5/16" | 3/8" |
| 3/4" | 19.050 | 10 | 12 | 10 | 16 | 1 1/8" | 9/16" | 3/8" | 3/8" | 1/2" |
| 7/8" | 22.225 | 9 | 11 | 9 | 14 | 1 3/8" | 9/16" | 1/2" | 1/2" | — |
| 1" | 25.400 | 8 | 10 | 8 | 12 | 1 1/2" | 5/8" | 9/16" | 9/16" | — |
| 1 1/8" | 28.575 | 7 | 9 | 7 | 12 | 1 11/16" | 3/4" | 5/8" | 9/16" | — |
| 1 1/4" | 31.750 | 7 | 9 | 7 | 12 | 1 7/8" | 3/4" | 5/8" | 5/8" | — |
| 1 3/8" | 34.925 | 6 | 8 | 6 | 12 | 2 1/16" | 3/4" | — | 5/8" | — |
| 1 1/2" | 38.100 | 6 | 8 | 6 | 12 | 2 1/4" | 1" | — | 3/4" | — |
| 1 5/8" | 41.275 | 5 | 8 | — | — | — | — | — | — | — |
| 1 3/4" | 44.450 | 5 | 7 | 5 | 12 | — | 1 1/4" | — | — | — |
| 2" | 50.800 | 4.5 | 7 | 4.5 | 12 | — | 1 3/8" | — | — | — |
Inch to millimetre. The exact size of each inch fastener in mm, and the metric size usually used in its place.
| Inch Size | Exact (mm) | Nearest Metric Size |
|---|---|---|
| 1/16" | 1.587 | M1.5 |
| 3/32" | 2.381 | M2.5 |
| 1/8" | 3.175 | M3 |
| 5/32" | 3.969 | M4 |
| 3/16" | 4.762 | M5 |
| 1/4" | 6.350 | M6 |
| 5/16" | 7.938 | M8 |
| 3/8" | 9.525 | M10 |
| 7/16" | 11.112 | — |
| 1/2" | 12.700 | M12 |
| 9/16" | 14.287 | M14 |
| 5/8" | 15.875 | M16 |
| 11/16" | 17.462 | M18 |
| 3/4" | 19.050 | M20 |
| 7/8" | 22.225 | M22 |
| 1" | 25.400 | M24 |
| 1 1/8" | 28.575 | M27 |
| 1 1/4" | 31.750 | M30 |
| 1 3/8" | 34.925 | M33 |
| 1 1/2" | 38.100 | M36 |
| — | — | M39 |
| 1 5/8" | 41.275 | M42 |
| 1 3/4" | 44.450 | M45 |
| 2" | 50.800 | M48 |
| — | — | M52 |
| 2 1/4" | 57.150 | M56 |
| — | — | M60 |
| 2 1/2" | 63.500 | M64 |
Standard Wire Gauge (SWG). Thickness of wire and sheet by gauge number — a smaller number is thicker.
| SWG | Inch | mm | Step per Gauge |
|---|---|---|---|
| 7/0 | 0.5 | 12.7 | 0.036"/gauge |
| 6/0 | 0.464 | 11.786 | 0.032"/gauge |
| 5/0 | 0.432 | 10.973 | |
| 4/0 | 0.4 | 10.16 | 0.028"/gauge |
| 3/0 | 0.372 | 9.449 | 0.024"/gauge |
| 2/0 | 0.348 | 8.839 | |
| 0 | 0.324 | 8.23 | |
| 1 | 0.3 | 7.62 | |
| 2 | 0.276 | 7.01 | |
| 3 | 0.252 | 6.401 | 0.020"/gauge |
| 4 | 0.232 | 5.893 | |
| 5 | 0.212 | 5.385 | |
| 6 | 0.192 | 4.877 | 0.016"/gauge |
| 7 | 0.176 | 4.47 | |
| 8 | 0.16 | 4.064 | |
| 9 | 0.144 | 3.658 | |
| 10 | 0.128 | 3.251 | 0.012"/gauge |
| 11 | 0.116 | 2.946 | |
| 12 | 0.104 | 2.642 | |
| 13 | 0.092 | 2.337 | |
| 14 | 0.08 | 2.032 | 0.008"/gauge |
| 15 | 0.072 | 1.829 | |
| 16 | 0.064 | 1.626 | |
| 17 | 0.056 | 1.422 | |
| 18 | 0.048 | 1.219 | |
| 19 | 0.04 | 1.016 | 0.004"/gauge |
| 20 | 0.036 | 0.914 | |
| 21 | 0.032 | 0.813 | |
| 22 | 0.028 | 0.711 | |
| 23 | 0.024 | 0.61 | 0.002"/gauge |
| 24 | 0.022 | 0.559 | |
| 25 | 0.02 | 0.508 | |
| 26 | 0.018 | 0.4572 | 0.0016"/gauge |
| 27 | 0.0164 | 0.4166 |
Please note: values are standard reference sizes; actual products can vary by manufacturer and standard. Ask us to confirm before ordering critical parts.