3-1/2-4 UNC Thread Specifications
Complete dimensions for 3-1/2-4 UNC (Unified National Coarse) thread per ASME B1.1. TPI: 4, Pitch: 0.25" (6.35 mm).
Thread Dimensions
| Designation | 3-1/2-4 UNC |
| Threads Per Inch (TPI) | 4 |
| Pitch | 0.25" (6.35 mm) |
| Major Diameter | 3.5" (88.9 mm) |
| Pitch Diameter | 3.3376" (84.776 mm) |
| Minor Diameter (External) | 3.1933" (81.109 mm) |
| Minor Diameter (Internal) | 3.2294" (82.026 mm) |
| Thread Depth | 0.13532" (3.437 mm) |
| Tensile Stress Area | 8.32862 in² (5373.3 mm²) |
Tap Drill Size
Recommended tap drill: 3-15/64" (3.2344" / 82.15 mm)
Calculated minor diameter (internal): 3.2294" (82.03 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 | 458,074 | 616,318 |
| Grade 5 | 85,000 | 120,000 | 707,933 | 999,434 |
| Grade 8 | 120,000 | 150,000 | 999,434 | 1,249,293 |
Common Applications
- Industrial and structural applications
- Coarse thread applications