3-4 UNC Thread Specifications
Complete dimensions for 3-4 UNC (Unified National Coarse) thread per ASME B1.1. TPI: 4, Pitch: 0.25" (6.35 mm).
Thread Dimensions
| Designation | 3-4 UNC |
| Threads Per Inch (TPI) | 4 |
| Pitch | 0.25" (6.35 mm) |
| Major Diameter | 3" (76.2 mm) |
| Pitch Diameter | 2.8376" (72.076 mm) |
| Minor Diameter (External) | 2.6933" (68.409 mm) |
| Minor Diameter (Internal) | 2.7294" (69.326 mm) |
| Thread Depth | 0.13532" (3.437 mm) |
| Tensile Stress Area | 5.96737 in² (3849.9 mm²) |
Tap Drill Size
Recommended tap drill: 2-47/64" (2.7344" / 69.45 mm)
Calculated minor diameter (internal): 2.7294" (69.33 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 | 328,205 | 441,585 |
| Grade 5 | 85,000 | 120,000 | 507,226 | 716,084 |
| Grade 8 | 120,000 | 150,000 | 716,084 | 895,106 |
Common Applications
- Industrial and structural applications
- Coarse thread applications