A wrench size isn’t the bolt’s diameter — it’s the distance across the flats of the head (or nut). A ½″ bolt doesn’t take a ½″ wrench; it takes a ¾″ one. The same size fits the matching nut. Heavy-hex bolts — the thicker structural style — have larger heads, so they need a bigger wrench than a standard bolt of the same diameter.
| Bolt diameter | Standard hex — wrench / socket | Heavy hex — wrench / socket |
|---|---|---|
| 1/4″ | 7/16″ | — |
| 5/16″ | 1/2″ | — |
| 3/8″ | 9/16″ | — |
| 7/16″ | 5/8″ | — |
| 1/2″ | 3/4″ | 7/8″ |
| 9/16″ | 13/16″ | 15/16″ |
| 5/8″ | 15/16″ | 1-1/16″ |
| 3/4″ | 1-1/8″ | 1-1/4″ |
| 7/8″ | 1-5/16″ | 1-7/16″ |
| 1″ | 1-1/2″ | 1-5/8″ |
| 1-1/8″ | 1-11/16″ | 1-13/16″ |
| 1-1/4″ | 1-7/8″ | 2″ |
| 1-3/8″ | 2-1/16″ | 2-3/16″ |
| 1-1/2″ | 2-1/4″ | 2-3/8″ |
The nut matches the bolt head. A finished hex nut takes the same wrench size as a standard hex bolt of the same diameter, so one size covers both ends of the joint.
Square heads and lag bolts use the same across-flats sizes as standard hex, so this chart works for them too. If you’ve got a head style that isn’t here, bring it by and we’ll size it.
