5/8-18 UNF Thread Specifications
Complete dimensions for 5/8-18 UNF (Unified National Fine) thread per ASME B1.1. TPI: 18, Pitch: 0.05556" (1.411 mm).
Thread Dimensions
| Designation | 5/8-18 UNF |
| Threads Per Inch (TPI) | 18 |
| Pitch | 0.05556" (1.411 mm) |
| Major Diameter | 0.625" (15.875 mm) |
| Pitch Diameter | 0.5889" (14.958 mm) |
| Minor Diameter (External) | 0.5568" (14.144 mm) |
| Minor Diameter (Internal) | 0.5649" (14.347 mm) |
| Thread Depth | 0.03007" (0.764 mm) |
| Tensile Stress Area | 0.25596 in² (165.1 mm²) |
Tap Drill Size
Recommended tap drill: 9/16" (0.5625" / 14.29 mm)
Calculated minor diameter (internal): 0.5649" (14.35 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 | 14,078 | 18,941 |
| Grade 5 | 85,000 | 120,000 | 21,757 | 30,715 |
| Grade 8 | 120,000 | 150,000 | 30,715 | 38,394 |
Same Size, Different Series
Common Applications
- Structural connections, heavy equipment, flanges
- Fine thread applications