Quick-reference torque values for 5/16" bolts across all SAE grades. Dry steel, UNC thread.
Values assume dry/plain steel (K = 0.20) and UNC thread. See full details →
A dry 5/16" Grade 5 bolt takes 17.4 ft·lbs (23.6 N·m) on the coarse 18 TPI thread. Oiled, that falls to 13.0 ft·lbs; the dry figure on an oiled bolt overshoots the intended clamp load by about 34%. Grade 8 needs 24.6 ft·lbs (41% more), and the fine 24 TPI thread raises the Grade 5 figure to 19.3 ft·lbs.
5/16" bolts are everywhere in automotive and equipment work. Grade 5 is the usual choice; Grade 8 goes on suspension, driveline and anything that sees shock load. Oiling the threads cuts the required torque by a quarter, not far short of the difference between Grade 5 and Grade 8, so knowing whether the threads are lubricated matters as much as knowing the grade.
ft·lbs unless noted. Clamp load is the 75%-of-proof preload in lbs.
| UNC (coarse) | 5/16"-18 |
| UNF (fine) | 5/16"-24 |
| Stress area (UNC / UNF) | 0.0524 / 0.058 in² |
| Hex wrench size | 1/2" (hex cap screw, ASME B18.2.1) |
| Tap drill (UNC / UNF) | F / I |
Threads per ASME B1.1; tap drills for about 75% thread engagement.