1-8 UNC Thread Specifications
Complete dimensions for 1-8 UNC (Unified National Coarse) thread per ASME B1.1. TPI: 8, Pitch: 0.125" (3.175 mm).
Thread Dimensions
| Designation | 1-8 UNC |
| Threads Per Inch (TPI) | 8 |
| Pitch | 0.125" (3.175 mm) |
| Major Diameter | 1" (25.4 mm) |
| Pitch Diameter | 0.9188" (23.338 mm) |
| Minor Diameter (External) | 0.8466" (21.505 mm) |
| Minor Diameter (Internal) | 0.8647" (21.963 mm) |
| Thread Depth | 0.06766" (1.719 mm) |
| Tensile Stress Area | 0.60575 in² (390.8 mm²) |
Tap Drill Size
Recommended tap drill: 7/8" (0.8750" / 22.22 mm)
Calculated minor diameter (internal): 0.8647" (21.96 mm)
Proof Loads by SAE Grade
| Grade | Proof Stress (psi) | Tensile Strength (psi) | Proof Load (lbf) | Tensile Load (lbf) |
|---|---|---|---|---|
| Grade 2 | 33,000 | 60,000 | 19,990 | 36,345 |
| Grade 5 | 85,000 | 120,000 | 51,488 | 72,689 |
| Grade 8 | 120,000 | 150,000 | 72,689 | 90,862 |
Same Size, Different Series
Common Applications
- Heavy structural, foundation bolts, large machinery
- Coarse thread applications