Quick-reference torque values for 1/2" 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 1/2" Grade 5 bolt takes 75.4 ft·lbs (102.2 N·m) on the coarse 13 TPI thread. Oiled, that falls to 56.5 ft·lbs; the dry figure on an oiled bolt overshoots the intended clamp load by about 33%. Grade 8 needs 106.4 ft·lbs (41% more), and the fine 20 TPI thread raises the Grade 5 figure to 85.0 ft·lbs.
1/2" 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) | 1/2"-13 |
| UNF (fine) | 1/2"-20 |
| Stress area (UNC / UNF) | 0.1419 / 0.1599 in² |
| Hex wrench size | 3/4" (hex cap screw, ASME B18.2.1) |
| Tap drill (UNC / UNF) | 27/64" / 29/64" |
Threads per ASME B1.1; tap drills for about 75% thread engagement.