1-8 UNC Thread Specifications
Complete dimensions for 1-8 UNC 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 | 0.59954 in² (386.8 mm²) |
Tap Drill Size
Recommended tap drill: 55/64" (0.8594" / 21.83 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 | 55,000 | 74,000 | 32,975 | 44,366 |
| Grade 5 | 85,000 | 120,000 | 50,961 | 71,945 |
| Grade 8 | 120,000 | 150,000 | 71,945 | 89,931 |
Same Size, Different Series
Common Applications
- Heavy structural, foundation bolts, large machinery
- Coarse thread applications