5/16 inch bolt torque
A 5/16-18 bolt takes 11 ft-lb in Grade 2, 17 in Grade 5 and 25 in Grade 8, dry, at 75% of proof load; the 5/16-24 fine thread takes 12, 19 and 27. 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 |
|---|---|---|---|---|---|---|
| 5/16-18UNC (coarse) | Grade 2 | 11.315.3 | 11.315.3 | 8.411.4 | 5.67.6 | 2,162 lbf9.6 kN |
| Grade 5 | 17.423.6 | 17.423.6 | 13.017.7 | 8.711.8 | 3,341 lbf14.9 kN | |
| Grade 8 | 24.633.3 | 24.633.3 | 18.425.0 | 12.316.7 | 4,716 lbf21.0 kN | |
| 5/16-24UNF (fine) | Grade 2 | 12.516.9 | 12.516.9 | 9.412.7 | 6.28.5 | 2,397 lbf10.7 kN |
| Grade 5 | 19.326.2 | 19.326.2 | 14.519.6 | 9.613.1 | 3,704 lbf16.5 kN | |
| Grade 8 | 27.236.9 | 27.236.9 | 20.427.7 | 13.618.5 | 5,229 lbf23.3 kN |
Work out 5/16 inch torque
Change grade, threads or preload
5/16-18 Grade 5, dry, plain steel
17.4ft-lb23.6N·m
209 in-lb
- Clamp load
- 3,341 lbf (14.9 kN)
- Proof load
- 4,454 lbf
The working
- Tensile stress area. A = 0.7854 × (D − 0.9743 ÷ n)² = 0.7854 × (0.3125 − 0.9743 ÷ 18)² = 0.0524 in²
- Proof load. Grade 5 proof stress is 85,000 psi, so A × stress = 4,454 lbf.
- Clamp load. 75% of proof load = 3,341 lbf.
- Torque. T = K × D × F = 0.2 × 0.3125 in × 3,341 lbf = 209 in-lb ÷ 12 = 17.4 ft-lb (23.6 N·m).
Where the 5/16-18 numbers come from
The 5/16-18 UNC (coarse) thread has a tensile stress area of 0.0524 in². A Grade 8 bolt’s proof stress is 120,000 psi, so its proof load is 6,288 lbf, and 75% of that is a clamp load of 4,716 lbf.
Torque = K × D × F = 0.20 × 0.3125 in × 4,716 lbf = 295 in-lb, or 24.6 ft-lb (33.3 N·m) dry. With oil (K 0.15) it’s 18.4 ft-lb (25.0 N·m).
Other sizes
All sizes on one page: the SAE bolt torque chart.
Questions
What torque for a 5/16-18 Grade 8 bolt?
24.6 ft-lb (33.3 N·m) dry and 18.4 ft-lb (25.0 N·m) oiled, at 75% of proof load. That clamps the joint with 4,716 lbf (21.0 kN).
What torque for a 5/16-18 Grade 5 bolt?
17.4 ft-lb (23.6 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 5/16-24 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.