Quick-reference torque values for 7/8" 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 7/8" Grade 5 bolt takes 429.5 ft·lbs (582.3 N·m) on the coarse 9 TPI thread. Oiled, that falls to 322.1 ft·lbs; the dry figure on an oiled bolt overshoots the intended clamp load by about 33%. Grade 8 needs 606.4 ft·lbs (41% more), and the fine 14 TPI thread raises the Grade 5 figure to 473.2 ft·lbs.
At 7/8", torques are into 1/2" drive and 3/4" drive territory. SAE J429 drops the Grade 2 proof stress from 55 to 33 ksi above 3/4", and Grade 5 from 85 to 74 ksi above 1", so the grades do not scale evenly through this range. Structural connections at this diameter are normally ASTM F3125 (A325/A490) bolts installed by turn-of-nut rather than by torque.
ft·lbs unless noted. Clamp load is the 75%-of-proof preload in lbs.
| UNC (coarse) | 7/8"-9 |
| UNF (fine) | 7/8"-14 |
| Stress area (UNC / UNF) | 0.462 / 0.509 in² |
| Hex wrench size | 1-5/16" (hex cap screw, ASME B18.2.1) |
| Tap drill (UNC / UNF) | 49/64" / 13/16" |
Threads per ASME B1.1; tap drills for about 75% thread engagement.