7/8 inch bolt torque
A 7/8-9 bolt takes 167 ft-lb in Grade 2, 430 in Grade 5 and 606 in Grade 8, dry, at 75% of proof load; the 7/8-14 fine thread takes 184, 473 and 668. Oiled threads take a quarter less.
Sources checked
| Thread | Grade | DryK 0.20 | Zinc platedK 0.20 | OiledK 0.15 | WaxedK 0.10 | Clamp load |
|---|---|---|---|---|---|---|
| 7/8-9UNC (coarse) | Grade 2 | 167226 | 167226 | 125170 | 83.4113 | 11,435 lbf50.9 kN |
| Grade 5 | 430582 | 430582 | 322437 | 215291 | 29,453 lbf131.0 kN | |
| Grade 8 | 606822 | 606822 | 455617 | 303411 | 41,580 lbf185.0 kN | |
| 7/8-14UNF (fine) | Grade 2 | 184249 | 184249 | 138187 | 91.9125 | 12,598 lbf56.0 kN |
| Grade 5 | 473642 | 473642 | 355481 | 237321 | 32,449 lbf144.3 kN | |
| Grade 8 | 668906 | 668906 | 501679 | 334453 | 45,810 lbf203.8 kN |
Work out 7/8 inch torque
Change grade, threads or preload
7/8-9 Grade 5, dry, plain steel
430ft-lb582N·m
- Clamp load
- 29,453 lbf (131.0 kN)
- Proof load
- 39,270 lbf
The working
- Tensile stress area. A = 0.7854 × (D − 0.9743 ÷ n)² = 0.7854 × (0.875 − 0.9743 ÷ 9)² = 0.462 in²
- Proof load. Grade 5 proof stress is 85,000 psi, so A × stress = 39,270 lbf.
- Clamp load. 75% of proof load = 29,453 lbf.
- Torque. T = K × D × F = 0.2 × 0.875 in × 29,453 lbf = 5,154 in-lb ÷ 12 = 430 ft-lb (582 N·m).
Where the 7/8-9 numbers come from
The 7/8-9 UNC (coarse) thread has a tensile stress area of 0.462 in². A Grade 8 bolt’s proof stress is 120,000 psi, so its proof load is 55,440 lbf, and 75% of that is a clamp load of 41,580 lbf.
Torque = K × D × F = 0.20 × 0.875 in × 41,580 lbf = 7,277 in-lb, or 606 ft-lb (822 N·m) dry. With oil (K 0.15) it’s 455 ft-lb (617 N·m).
Other sizes
All sizes on one page: the SAE bolt torque chart.
Questions
What torque for a 7/8-9 Grade 8 bolt?
606 ft-lb (822 N·m) dry and 455 ft-lb (617 N·m) oiled, at 75% of proof load. That clamps the joint with 41,580 lbf (185.0 kN).
What torque for a 7/8-9 Grade 5 bolt?
430 ft-lb (582 N·m) dry, at 75% of proof load; a quarter less with oiled threads.
Coarse or fine thread?
Use whichever the bolt has. The fine 7/8-14 thread has a bigger stress area than the coarse one, so it takes slightly more torque for the same clamp. A thread gauge settles it.
Does this apply to wheel nuts or engine bolts?
No. Use the vehicle maker’s value for those: see lug nut torque by vehicle. These numbers are for general-purpose steel bolts where no spec exists.
Sources
- Portland Bolt: SAE J429: proof load, yield and tensile strength for Grades 2, 5 and 8 (checked October 14, 2026)
- Portland Bolt: Thread pitch chart: UNC and UNF threads per inch and tensile stress areas (checked October 14, 2026)
- Fastenal: Mechanical properties of inch fasteners, with UNC and UNF tensile stress areas (checked October 14, 2026)
- Engineering Toolbox: Threaded bolts: tensile stress area formulas for unified and ISO metric threads (checked October 14, 2026)
- Fastenal: Torque–tension relationship for A307 A, Grade 5, 8 and 9 coarse thread bolts (75% of proof load; K 0.15 and 0.20) (checked October 14, 2026)
- Portland Bolt: Bolt torque chart: T = KDP at 75% of proof load, with K for plain, waxed and galvanized bolts (checked October 14, 2026)
Spotted a number that doesn’t match your manual or a source? Tell us; corrections are logged on the sources page.