American Wrench Size Chart
Quick answer: American wrench sizes are usually SAE fractional inch sizes. The wrench fits the head or nut across the flats, not the threaded bolt diameter. For example, a 1/2 in standard hex bolt commonly takes a 3/4 in wrench, while a 1/2 in heavy-hex bolt takes a 7/8 in wrench.
SAE Bolt And Wrench Size Chart
| #6 | 1/4 in | - | Small machine screw |
|---|---|---|---|
| #8 | 1/4 in | - | Small machine screw |
| #10 | 5/16 in | - | Small machine screw |
| #12 | 5/16 in | - | Small machine screw |
| 1/4 in | 7/16 in or 3/8 in | - | Head style can vary |
| 5/16 in | 1/2 in | - | Common light hardware |
| 3/8 in | 9/16 in | - | Common shop hardware |
| 7/16 in | 5/8 in | - | Common shop hardware |
| 1/2 in | 3/4 in | 7/8 in | Heavy hex uses a larger wrench |
| 9/16 in | 13/16 in | - | Check the fastener head |
| 5/8 in | 15/16 in | 1-1/16 in | Large hardware |
| 3/4 in | 1-1/8 in | 1-1/4 in | Large hardware |
| 7/8 in | 1-5/16 in | 1-7/16 in | Heavy hardware |
| 1 in | 1-1/2 in | 1-5/8 in | Heavy hardware |
| 1-1/8 in | 1-11/16 in | 1-3/4 in | Heavy hardware |
| 1-1/4 in | 1-7/8 in | 2 in | Industrial hardware |
16 rows
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SAE To Metric Close Reference
| 3/8 in | 0.375 | 9.53 mm | Close to 10 mm, not identical |
|---|---|---|---|
| 7/16 in | 0.438 | 11.11 mm | Close to 11 mm |
| 1/2 in | 0.500 | 12.70 mm | Close to 13 mm, not identical |
| 9/16 in | 0.563 | 14.29 mm | Close to 14 mm |
| 5/8 in | 0.625 | 15.88 mm | Close to 16 mm |
| 3/4 in | 0.750 | 19.05 mm | Close to 19 mm |
| 13/16 in | 0.813 | 20.64 mm | Close to 21 mm |
| 7/8 in | 0.875 | 22.23 mm | Close to 22 mm |
8 rows
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Wrench Fit Tips
- Measure across the flats when the correct size is uncertain.
- Use a 6-point socket on stuck or rusty fasteners.
- Do not force a loose metric substitute onto SAE hardware under high torque.
- Check the bolt spanner size chart for metric comparisons.
Source Notes
Hex-head and heavy-hex wrench sizes are based on Bolt Depot’s US bolt head and wrench chart. Metric equivalents use the exact 25.4 mm per inch definition from NIST. Confirm the actual head or nut across its flats; head style and fastener standards can vary.
