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UNC & UNF Thread Chart
ASME B1.1 unified inch screw threads, the most common sizes.
UNC (Coarse)
| Size | TPI | Pitch (mm) | Minor dia (in) | Tap drill |
|---|---|---|---|---|
| 1/4 | 20 | 1.27 | 0.185 | #7 |
| 5/16 | 18 | 1.41 | 0.240 | F |
| 3/8 | 16 | 1.59 | 0.294 | 5/16 |
| 7/16 | 14 | 1.81 | 0.344 | U |
| 1/2 | 13 | 1.95 | 0.400 | 3/8 |
| 9/16 | 12 | 2.12 | 0.454 | 31/64 |
| 5/8 | 11 | 2.31 | 0.507 | 17/32 |
| 3/4 | 10 | 2.54 | 0.620 | 21/32 |
| 7/8 | 9 | 2.82 | 0.731 | 49/64 |
| 1 | 8 | 3.18 | 0.837 | 7/8 |
UNF (Fine)
| Size | TPI | Tap drill |
|---|---|---|
| 1/4 | 28 | #3 |
| 5/16 | 24 | I |
| 3/8 | 24 | Q |
| 1/2 | 20 | 7/16 |
| 5/8 | 18 | 9/16 |
| 3/4 | 16 | 11/16 |
FAQ
UNC or UNF — which is stronger?
UNF has a larger minor-to-major ratio, giving higher tensile strength; UNC taps easier and resists stripping in soft materials.
What does 1/4-20 mean?
1/4 inch major diameter, 20 threads per inch (pitch = 1/20 in = 1.27 mm).