Bolt Chart With Wrench Size
Quick answer: standard hex bolt wrench size is measured across the flats of the bolt head. For example, a 1/4-inch hex bolt commonly uses a 7/16-inch wrench, a 3/8-inch bolt commonly uses a 9/16-inch wrench, and a 1/2-inch bolt commonly uses a 3/4-inch wrench. Heavy hex bolts use larger wrench sizes than standard hex bolts.
Inch Bolt Wrench Size Chart
| Bolt diameter | Standard hex / lag / square wrench size | Heavy hex wrench size | Notes |
|---|---|---|---|
| #6 | 1/4 in | – | Small machine screw/bolt range |
| #8 | 1/4 in | – | Small machine screw/bolt range |
| #10 | 5/16 in | – | Small fastener range |
| #12 | 5/16 in | – | Small fastener range |
| 1/4 in | 7/16 in or 3/8 in | – | Head style can vary on small bolts |
| 5/16 in | 1/2 in | – | Common light-duty hardware |
| 3/8 in | 9/16 in | – | Very common garage size |
| 7/16 in | 5/8 in | – | Common structural/hardware size |
| 1/2 in | 3/4 in | 7/8 in | Heavy hex is larger across flats |
| 9/16 in | 13/16 in | – | Less common in small kits |
| 5/8 in | 15/16 in | 1-1/16 in | Common heavier fastener |
| 3/4 in | 1-1/8 in | 1-1/4 in | Large hardware and structural work |
| 7/8 in | 1-5/16 in | 1-7/16 in | Large hardware |
| 1 in | 1-1/2 in | 1-5/8 in | Large hardware |
| 1-1/8 in | 1-11/16 in | 1-3/4 in | Large structural fastener range |
| 1-1/4 in | 1-7/8 in | 2 in | Large structural fastener range |
Standard Hex vs Heavy Hex
A heavy hex bolt has a larger head across the flats than a standard hex bolt of the same diameter. That is why a 1/2-inch standard hex bolt may use a 3/4-inch wrench while a 1/2-inch heavy hex bolt uses a 7/8-inch wrench. When working with structural bolts, do not assume the wrench size from bolt diameter alone.
How To Avoid Rounding Bolt Heads
- Use a 6-point socket or box wrench on stubborn bolts.
- Clean rust and paint from the head before sizing the wrench.
- Confirm whether the fastener is inch or metric.
- Use the heavy-hex column when the bolt head is visibly larger than a standard hex head.
- Do not use an adjustable wrench for high-torque removal unless there is no better option.
Related references: socket sizes in order, American wrench size chart, and Allen wrench size chart.
Source Notes
Wrench-size references were checked against inch fastener wrench charts and heavy-hex references based on ANSI/ASME bolt dimensions. Use manufacturer drawings for critical structural or engineered connections.
