Standard coarse threads: 1/4-20, 5/16-18, 3/8-16, 1/2-13 UNC; M6 x 1.0, M8 x 1.25, M10 x 1.5, M12 x 1.75 metric. Pitch in mm = 25.4 / TPI, so 20 TPI is 1.27 mm and 13 TPI is 1.954 mm.
Thread pitch for every standard size, with the equivalent in the other system. To identify an unknown thread use a pitch gauge and the thread pitch converter.
Tools that go with this chart
Unified inch threads
| Thread | Series | TPI | Pitch (mm) | Major (in) | Minor (in, basic) |
|---|---|---|---|---|---|
| #0-80 | UNF | 80 | 0.318 | 0.0600 | 0.0438 |
| #1-64 | UNC | 64 | 0.397 | 0.0730 | 0.0527 |
| #1-72 | UNF | 72 | 0.353 | 0.0730 | 0.0550 |
| #2-56 | UNC | 56 | 0.454 | 0.0860 | 0.0628 |
| #2-64 | UNF | 64 | 0.397 | 0.0860 | 0.0657 |
| #3-48 | UNC | 48 | 0.529 | 0.0990 | 0.0719 |
| #3-56 | UNF | 56 | 0.454 | 0.0990 | 0.0758 |
| #4-40 | UNC | 40 | 0.635 | 0.1120 | 0.0795 |
| #4-48 | UNF | 48 | 0.529 | 0.1120 | 0.0849 |
| #5-40 | UNC | 40 | 0.635 | 0.1250 | 0.0925 |
| #5-44 | UNF | 44 | 0.577 | 0.1250 | 0.0955 |
| #6-32 | UNC | 32 | 0.794 | 0.1380 | 0.0974 |
| #6-40 | UNF | 40 | 0.635 | 0.1380 | 0.1055 |
| #8-32 | UNC | 32 | 0.794 | 0.1640 | 0.1234 |
| #8-36 | UNF | 36 | 0.706 | 0.1640 | 0.1279 |
| #10-24 | UNC | 24 | 1.058 | 0.1900 | 0.1359 |
| #10-32 | UNF | 32 | 0.794 | 0.1900 | 0.1494 |
| #12-24 | UNC | 24 | 1.058 | 0.2160 | 0.1619 |
| #12-28 | UNF | 28 | 0.907 | 0.2160 | 0.1696 |
| 1/4-20 | UNC | 20 | 1.270 | 0.2500 | 0.1850 |
| 1/4-28 | UNF | 28 | 0.907 | 0.2500 | 0.2036 |
| 5/16-18 | UNC | 18 | 1.411 | 0.3125 | 0.2403 |
| 5/16-24 | UNF | 24 | 1.058 | 0.3125 | 0.2584 |
| 3/8-16 | UNC | 16 | 1.587 | 0.3750 | 0.2938 |
| 3/8-24 | UNF | 24 | 1.058 | 0.3750 | 0.3209 |
| 7/16-14 | UNC | 14 | 1.814 | 0.4375 | 0.3447 |
| 7/16-20 | UNF | 20 | 1.270 | 0.4375 | 0.3725 |
| 1/2-13 | UNC | 13 | 1.954 | 0.5000 | 0.4001 |
| 1/2-20 | UNF | 20 | 1.270 | 0.5000 | 0.4350 |
| 9/16-12 | UNC | 12 | 2.117 | 0.5625 | 0.4542 |
| 9/16-18 | UNF | 18 | 1.411 | 0.5625 | 0.4903 |
| 5/8-11 | UNC | 11 | 2.309 | 0.6250 | 0.5069 |
| 5/8-18 | UNF | 18 | 1.411 | 0.6250 | 0.5528 |
| 3/4-10 | UNC | 10 | 2.540 | 0.7500 | 0.6201 |
| 3/4-16 | UNF | 16 | 1.587 | 0.7500 | 0.6688 |
| 7/8-9 | UNC | 9 | 2.822 | 0.8750 | 0.7307 |
| 7/8-14 | UNF | 14 | 1.814 | 0.8750 | 0.7822 |
| 1-8 | UNC | 8 | 3.175 | 1.0000 | 0.8376 |
| 1-12 | UNF | 12 | 2.117 | 1.0000 | 0.8918 |
| 1-14 | UNS | 14 | 1.814 | 1.0000 | 0.9072 |
ISO metric threads
| Thread | Series | Pitch (mm) | Equivalent TPI | Major (mm) | Minor (mm, basic) |
|---|---|---|---|---|---|
| M1.6x0.35 | coarse | 0.35 | 72.57 | 1.6 | 1.221 |
| M2x0.4 | coarse | 0.4 | 63.50 | 2 | 1.567 |
| M2.5x0.45 | coarse | 0.45 | 56.44 | 2.5 | 2.013 |
| M3x0.5 | coarse | 0.5 | 50.80 | 3 | 2.459 |
| M3x0.35 | fine | 0.35 | 72.57 | 3 | 2.621 |
| M3.5x0.6 | coarse | 0.6 | 42.33 | 3.5 | 2.851 |
| M4x0.7 | coarse | 0.7 | 36.29 | 4 | 3.242 |
| M4x0.5 | fine | 0.5 | 50.80 | 4 | 3.459 |
| M5x0.8 | coarse | 0.8 | 31.75 | 5 | 4.134 |
| M5x0.5 | fine | 0.5 | 50.80 | 5 | 4.459 |
| M6x1 | coarse | 1 | 25.40 | 6 | 4.918 |
| M6x0.75 | fine | 0.75 | 33.87 | 6 | 5.188 |
| M8x1.25 | coarse | 1.25 | 20.32 | 8 | 6.647 |
| M8x1 | fine | 1 | 25.40 | 8 | 6.918 |
| M10x1.5 | coarse | 1.5 | 16.93 | 10 | 8.376 |
| M10x1.25 | fine | 1.25 | 20.32 | 10 | 8.647 |
| M10x1 | fine | 1 | 25.40 | 10 | 8.918 |
| M12x1.75 | coarse | 1.75 | 14.51 | 12 | 10.106 |
| M12x1.5 | fine | 1.5 | 16.93 | 12 | 10.376 |
| M12x1.25 | fine | 1.25 | 20.32 | 12 | 10.647 |
| M14x2 | coarse | 2 | 12.70 | 14 | 11.835 |
| M14x1.5 | fine | 1.5 | 16.93 | 14 | 12.376 |
| M16x2 | coarse | 2 | 12.70 | 16 | 13.835 |
| M16x1.5 | fine | 1.5 | 16.93 | 16 | 14.376 |
| M18x2.5 | coarse | 2.5 | 10.16 | 18 | 15.294 |
| M18x1.5 | fine | 1.5 | 16.93 | 18 | 16.376 |
| M20x2.5 | coarse | 2.5 | 10.16 | 20 | 17.294 |
| M20x1.5 | fine | 1.5 | 16.93 | 20 | 18.376 |
| M22x2.5 | coarse | 2.5 | 10.16 | 22 | 19.294 |
| M22x1.5 | fine | 1.5 | 16.93 | 22 | 20.376 |
| M24x3 | coarse | 3 | 8.47 | 24 | 20.753 |
| M24x2 | fine | 2 | 12.70 | 24 | 21.835 |
| M27x3 | coarse | 3 | 8.47 | 27 | 23.753 |
| M30x3.5 | coarse | 3.5 | 7.26 | 30 | 26.211 |
| M30x2 | fine | 2 | 12.70 | 30 | 27.835 |
| M36x4 | coarse | 4 | 6.35 | 36 | 31.670 |
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Frequently asked questions
What is the difference between UNC and UNF?
UNC (coarse) has fewer threads per inch at each diameter: 1/4-20 versus 1/4-28 UNF. Coarse threads assemble faster, tolerate dirt and damage, and hold better in soft materials like aluminum. Fine threads are stronger in tension for the same diameter, resist vibration loosening and allow finer adjustment.
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Figures are from published standards and handbook values, reproduced for convenience. Check critical dimensions against the standard or your tooling manufacturer.