Screw Thread Chart
Metric (ISO)
| Size | Coarse pitch (mm) | Tap drill (mm) | Fine pitch (mm) | Tap drill (mm) |
| M1.6 | 0.35 | 1.25 | - | - |
| M2 | 0.4 | 1.6 | - | - |
| M2.5 | 0.45 | 2.05 | - | - |
| M3 | 0.5 | 2.5 | - | - |
| M4 | 0.7 | 3.3 | - | - |
| M5 | 0.8 | 4.2 | - | - |
| M6 | 1 | 5 | - | - |
| M8 | 1.25 | 6.75 | 1 | 7 |
| M10 | 1.5 | 8.5 | 1.25 | 8.75 |
| M12 | 1.75 | 10.25 | 1.25 | 10.75 |
| M14 | 2 | 12 | 1.5 | 12.5 |
| M16 | 2 | 14 | 1.5 | 14.5 |
| M18 | 2.5 | 15.5 | 1.5 | 16.5 |
| M20 | 2.5 | 17.5 | 1.5 | 18.5 |
| M22 | 2.5 | 19.5 | 1.5 | 20.5 |
| M24 | 3 | 21 | 2 | 22 |
Unified (UNC / UNF)
| Size | Diameter (in) | UNC (TPI) | Tap drill (in) | UNF (TPI) | Tap drill (in) |
| #0 | 0.0600 | - | - | 80 | 0.0475 |
| #1 | 0.0730 | 64 | 0.0574 | 72 | 0.0591 |
| #2 | 0.0860 | 56 | 0.0681 | 64 | 0.0704 |
| #3 | 0.0990 | 48 | 0.0782 | 56 | 0.0811 |
| #4 | 0.1120 | 40 | 0.0870 | 48 | 0.0912 |
| #5 | 0.1250 | 40 | 0.1000 | 44 | 0.1023 |
| #6 | 0.1380 | 32 | 0.1068 | 40 | 0.1130 |
| #8 | 0.1640 | 32 | 0.1328 | 36 | 0.1362 |
| #10 | 0.1900 | 24 | 0.1483 | 32 | 0.1588 |
| #12 | 0.2160 | 24 | 0.1743 | 28 | 0.1803 |
| 1/4 | 0.2500 | 20 | 0.2000 | 28 | 0.2143 |
| 5/16 | 0.3125 | 18 | 0.2569 | 24 | 0.2708 |
| 3/8 | 0.3750 | 16 | 0.3125 | 24 | 0.3333 |
| 7/16 | 0.4375 | 14 | 0.3661 | 20 | 0.3875 |
| 1/2 | 0.5000 | 13 | 0.4231 | 20 | 0.4500 |
| 9/16 | 0.5625 | 12 | 0.4792 | 18 | 0.5069 |
| 5/8 | 0.6250 | 11 | 0.5341 | 18 | 0.5694 |
| 3/4 | 0.7500 | 10 | 0.6500 | 16 | 0.6875 |
| 7/8 | 0.8750 | 9 | 0.7639 | 14 | 0.8036 |
| 1 | 1.0000 | 8 | 0.8750 | 12 | 0.9167 |
How to use Screw Thread Chart
- Find the metric or unified size.
- Read the pitch or threads per inch, and the tap drill.
Frequently asked questions
How is the tap drill size worked out?
As the major diameter minus the pitch (metric) or minus 1 / TPI (unified), which gives about 75% thread. Round to the nearest drill you have.
What does M8 × 1.25 mean?
A metric thread 8 mm across with 1.25 mm between threads, which is the standard coarse pitch for M8.
What is the difference between coarse and fine threads?
Fine threads have a smaller pitch. They hold better in thin walls and adjust more finely, but cross-thread and strip more easily in soft materials.
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