3-3/4-4 UNC Thread Specifications
Complete dimensions for 3-3/4-4 UNC (Unified National Coarse) thread per ASME B1.1. TPI: 4, Pitch: 0.25" (6.35 mm).
Thread Dimensions
| Designation | 3-3/4-4 UNC |
| Threads Per Inch (TPI) | 4 |
| Pitch | 0.25" (6.35 mm) |
| Major Diameter | 3.75" (95.25 mm) |
| Pitch Diameter | 3.5876" (91.126 mm) |
| Minor Diameter (External) | 3.4433" (87.459 mm) |
| Minor Diameter (Internal) | 3.4794" (88.376 mm) |
| Thread Depth | 0.13532" (3.437 mm) |
| Tensile Stress Area | 9.65651 in² (6230.0 mm²) |
Tap Drill Size
Recommended tap drill: 3-31/64" (3.4844" / 88.5 mm)
Calculated minor diameter (internal): 3.4794" (88.38 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 | 531,108 | 714,582 |
| Grade 5 | 85,000 | 120,000 | 820,803 | 1,158,781 |
| Grade 8 | 120,000 | 150,000 | 1,158,781 | 1,448,477 |
Common Applications
- Industrial and structural applications
- Coarse thread applications