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.
FAQ
What’s the difference between a screw size chart and a fastener size chart? A fastener chart typically covers a broader range including bolts, nails, and other hardware with their standard diameters and lengths, while a screw-specific chart focuses on screw gauge, thread pitch, and length options for wood, sheet metal, or machine screws. When in doubt about a specific application, checking the fastener manufacturer’s load rating table is more reliable than a general size chart alone.
See the Nail Size Chart and Screw Size Chart.