1-3/8-18 UNEF Thread Specifications
Complete dimensions for 1-3/8-18 UNEF (Unified National Extra Fine) thread per ASME B1.1. TPI: 18, Pitch: 0.05556" (1.411 mm).
Thread Dimensions
| Designation | 1-3/8-18 UNEF |
| Threads Per Inch (TPI) | 18 |
| Pitch | 0.05556" (1.411 mm) |
| Major Diameter | 1.375" (34.925 mm) |
| Pitch Diameter | 1.3389" (34.008 mm) |
| Minor Diameter (External) | 1.3068" (33.194 mm) |
| Minor Diameter (Internal) | 1.3149" (33.397 mm) |
| Thread Depth | 0.03007" (0.764 mm) |
| Tensile Stress Area | 1.37029 in² (884.1 mm²) |
Tap Drill Size
Recommended tap drill: 1-5/16" (1.3125" / 33.34 mm)
Calculated minor diameter (internal): 1.3149" (33.4 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 | 75,366 | 101,401 |
| Grade 5 | 85,000 | 120,000 | 116,475 | 164,435 |
| Grade 8 | 120,000 | 150,000 | 164,435 | 205,544 |
Same Size, Different Series
Common Applications
- Precision assemblies
- Thin-wall tubing
- Aerospace fittings