5/16-18 UNC Thread Specifications
Complete dimensions for 5/16-18 UNC thread per ASME B1.1. TPI: 18, Pitch: 0.05556" (1.411 mm).
Thread Dimensions
| Designation | 5/16-18 UNC |
| Threads Per Inch (TPI) | 18 |
| Pitch | 0.05556" (1.411 mm) |
| Major Diameter | 0.3125" (7.938 mm) |
| Pitch Diameter | 0.2764" (7.021 mm) |
| Minor Diameter (External) | 0.2443" (6.206 mm) |
| Minor Diameter (Internal) | 0.2524" (6.41 mm) |
| Thread Depth | 0.03007" (0.764 mm) |
| Tensile Stress Area | 0.05162 in² (33.3 mm²) |
Tap Drill Size
Recommended tap drill: E (0.25" / 6.35 mm)
Calculated minor diameter (internal): 0.2524" (6.41 mm)
Proof Loads by SAE Grade
| Grade | Proof Stress (psi) | Tensile Strength (psi) | Proof Load (lbf) | Tensile Load (lbf) |
|---|---|---|---|---|
| Grade 2 | 55,000 | 74,000 | 2,839 | 3,820 |
| Grade 5 | 85,000 | 120,000 | 4,388 | 6,194 |
| Grade 8 | 120,000 | 150,000 | 6,194 | 7,743 |
Same Size, Different Series
Common Applications
- Machinery, automotive accessories, medium-duty brackets
- Coarse thread applications