Standard Hex Nut Sizes
These are the basic dimensions for standard hex nuts per ASME B18.2.2. The “width across flats” is what you need for wrench/socket sizing.
| Nominal Size | Threads/in (UNC) | Width Across Flats (in) | Width Across Corners (in) | Height (in) |
|---|---|---|---|---|
| 1/4″ | 20 | 7/16 | 0.505 | 7/32 |
| 5/16″ | 18 | 1/2 | 0.577 | 17/64 |
| 3/8″ | 16 | 9/16 | 0.650 | 21/64 |
| 7/16″ | 14 | 11/16 | 0.794 | 3/8 |
| 1/2″ | 13 | 3/4 | 0.866 | 7/16 |
| 9/16″ | 12 | 7/8 | 1.010 | 31/64 |
| 5/8″ | 11 | 15/16 | 1.083 | 35/64 |
| 3/4″ | 10 | 1-1/8 | 1.299 | 41/64 |
| 7/8″ | 9 | 1-5/16 | 1.516 | 3/4 |
| 1″ | 8 | 1-1/2 | 1.732 | 55/64 |
| 1-1/8″ | 7 | 1-11/16 | 1.949 | 31/32 |
| 1-1/4″ | 7 | 1-7/8 | 2.165 | 1-1/16 |
| 1-1/2″ | 6 | 2-1/4 | 2.598 | 1-9/32 |
Quick Reference: Wrench Sizes
The wrench size for a standard hex nut is the width across flats. A common source of confusion: the wrench size does NOT match the bolt diameter. A 1/2″ bolt takes a 3/4″ wrench.
| Bolt Diameter | Wrench Size (US) | Wrench Size (Metric Equivalent) |
|---|---|---|
| 1/4″ | 7/16″ | 11mm |
| 5/16″ | 1/2″ | 13mm |
| 3/8″ | 9/16″ | 14mm |
| 1/2″ | 3/4″ | 19mm |
| 5/8″ | 15/16″ | 24mm |
| 3/4″ | 1-1/8″ | 29mm |
| 1″ | 1-1/2″ | 38mm |
For nut grades and mechanical properties, see Hex Nut Grade Identification.
Related: Hex Cap Bolt Dimensions | Flat Washer Dimensions