Bolt / Thread Sizes (SAE)
US Standard (SAE) bolt sizes: major diameter, threads per inch, minor diameter, and tap drill.
| Bolt | Major Diameter | TPI | Minor Diameter | Tap Drill |
|---|---|---|---|---|
| 1/4-20 | 0.25 | 20 | 0.185 | 0.201 |
| 1/4-28 | 0.25 | 28 | 0.196 | 0.213 |
| 5/16-18 | 0.3125 | 18 | 0.24 | 0.257 |
| 5/16-24 | 0.3125 | 24 | 0.252 | 0.272 |
| 3/8-16 | 0.375 | 16 | 0.294 | 0.313 |
| 3/8-24 | 0.375 | 24 | 0.314 | 0.332 |
| 7/16-14 | 0.4375 | 14 | 0.345 | 0.368 |
| 1/2-13 | 0.5 | 13 | 0.4 | 0.422 |
| 1/2-20 | 0.5 | 20 | 0.425 | 0.453 |
| 9/16-12 | 0.5625 | 12 | 0.454 | 0.484 |
| 5/8-11 | 0.625 | 11 | 0.507 | 0.547 |
| 5/8-18 | 0.625 | 18 | 0.533 | 0.578 |
| 3/4-10 | 0.75 | 10 | 0.62 | 0.672 |
| 3/4-16 | 0.75 | 16 | 0.647 | 0.703 |
| 7/8-9 | 0.875 | 9 | 0.731 | 0.781 |
| 1-8 | 1 | 8 | 0.838 | 0.906 |
| 1-12 | 1 | 12 | 0.87 | 0.938 |
About this lookup
- What is TPI?
- Threads Per Inch. Higher TPI = finer thread.
- UNC vs UNF?
- UNC (Unified National Coarse) is the standard. UNF (Fine) is shown as the second number in each pair (e.g. 1/4-28).