Bolts and machine screws are sized by diameter and thread count. This chart covers common coarse-thread (UNC) sizes used in construction and assembly.
| Size | Diameter | Threads/in (UNC) |
|---|---|---|
| #8 | 0.164 in | 32 |
| #10 | 0.190 in | 24 |
| 1/4 in | 0.250 in | 20 |
| 5/16 in | 0.3125 in | 18 |
| 3/8 in | 0.375 in | 16 |
| 1/2 in | 0.500 in | 13 |
| 5/8 in | 0.625 in | 11 |
Coarse vs fine. UNC (coarse) threads shown here are standard for wood and general construction. Match the thread pitch of bolt and nut, and the diameter to the load.
See the Nail Size Chart and Screw Size Chart.