Engineering Tools
Reference data for specifying and sourcing fasteners correctly — the numbers a procurement or design engineer actually needs.
Thread identification
Imperial thread series with their nearest metric equivalent — useful when a US or UK drawing specs an imperial thread you need to source or match.
American (UNC / UNF)
| Size | UNC (coarse) TPI | UNF (fine) TPI | Nearest metric |
|---|---|---|---|
| #6 (0.138") | 32 | 40 | M3.5 |
| #8 (0.164") | 32 | 36 | M4 |
| #10 (0.190") | 24 | 32 | M5 |
| 1/4" | 20 | 28 | M6 |
| 5/16" | 18 | 24 | M8 |
| 3/8" | 16 | 24 | M10 |
| 1/2" | 13 | 20 | M12 |
| 5/8" | 11 | 18 | M16 |
| 3/4" | 10 | 16 | M20 |
British (BSW / BSF)
| Size | BSW (Whitworth) TPI | BSF (fine) TPI |
|---|---|---|
| 1/4" | 20 | 26 |
| 5/16" | 18 | 22 |
| 3/8" | 16 | 20 |
| 1/2" | 12 | 16 |
| 5/8" | 11 | 14 |
| 3/4" | 10 | 12 |
TPI = threads per inch. UNC/UNF threads use a 60° thread angle like metric; BSW/BSF use a 55° Whitworth form — the two are not interchangeable even at a matching TPI.