Thread chart: UNC, UNF and metric
The common thread sizes and their pitches. Checked against several published charts.
Unified inch threads
| Size | Major diameter | UNC (threads per inch) | UNF (threads per inch) |
|---|---|---|---|
| #10 | .190 in | 24 | 32 |
| 1/4 | 1/4 in | 20 | 28 |
| 5/16 | 5/16 in | 18 | 24 |
| 3/8 | 3/8 in | 16 | 24 |
| 7/16 | 7/16 in | 14 | 20 |
| 1/2 | 1/2 in | 13 | 20 |
| 5/8 | 5/8 in | 11 | 18 |
| 3/4 | 3/4 in | 10 | 16 |
ISO metric threads
| Size | Coarse pitch (mm) | Common fine pitch (mm) |
|---|---|---|
| M4 | 0.7 | 0.5 |
| M5 | 0.8 | 0.5 |
| M6 | 1 | 0.75 |
| M8 | 1.25 | 1 |
| M10 | 1.5 | 1.25 |
| M12 | 1.75 | 1.25 |
| M16 | 2 | 1.5 |
| M20 | 2.5 | 1.5 |
| M24 | 3 | 2 |
Most metric sizes have more than one fine pitch. The one shown is a common choice.
Reading the callout
1/4-20 UNC-2A is a 1/4 inch coarse thread with 20 threads per inch, class 2, external. M10x1.5-6H is a 10 mm metric thread with a 1.5 mm pitch, tolerance class 6H, internal. When a metric callout has no pitch, the coarse pitch applies.