1/2 inch bolt torque
A 1/2-13 bolt takes 49 ft-lb in Grade 2, 75 in Grade 5 and 106 in Grade 8, dry, at 75% of proof load; the 1/2-20 fine thread takes 55, 85 and 120. 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 |
|---|---|---|---|---|---|---|
| 1/2-13UNC (coarse) | Grade 2 | 48.866.1 | 48.866.1 | 36.649.6 | 24.433.1 | 5,853 lbf26.0 kN |
| Grade 5 | 75.4102 | 75.4102 | 56.576.7 | 37.751.1 | 9,046 lbf40.2 kN | |
| Grade 8 | 106144 | 106144 | 79.8108 | 53.272.1 | 12,771 lbf56.8 kN | |
| 1/2-20UNF (fine) | Grade 2 | 55.074.6 | 55.074.6 | 41.355.9 | 27.537.3 | 6,600 lbf29.4 kN |
| Grade 5 | 85.0115 | 85.0115 | 63.886.4 | 42.557.6 | 10,200 lbf45.4 kN | |
| Grade 8 | 120163 | 120163 | 90.0122 | 60.081.3 | 14,400 lbf64.1 kN |
Work out 1/2 inch torque
Change grade, threads or preload
1/2-13 Grade 5, dry, plain steel
75.4ft-lb102N·m
- Clamp load
- 9,046 lbf (40.2 kN)
- Proof load
- 12,062 lbf
The working
- Tensile stress area. A = 0.7854 × (D − 0.9743 ÷ n)² = 0.7854 × (0.5 − 0.9743 ÷ 13)² = 0.1419 in²
- Proof load. Grade 5 proof stress is 85,000 psi, so A × stress = 12,062 lbf.
- Clamp load. 75% of proof load = 9,046 lbf.
- Torque. T = K × D × F = 0.2 × 0.5 in × 9,046 lbf = 905 in-lb ÷ 12 = 75.4 ft-lb (102 N·m).
Where the 1/2-13 numbers come from
The 1/2-13 UNC (coarse) thread has a tensile stress area of 0.1419 in². A Grade 8 bolt’s proof stress is 120,000 psi, so its proof load is 17,028 lbf, and 75% of that is a clamp load of 12,771 lbf.
Torque = K × D × F = 0.20 × 0.5 in × 12,771 lbf = 1,277 in-lb, or 106 ft-lb (144 N·m) dry. With oil (K 0.15) it’s 79.8 ft-lb (108 N·m).
Other sizes
All sizes on one page: the SAE bolt torque chart.
Questions
What torque for a 1/2-13 Grade 8 bolt?
106 ft-lb (144 N·m) dry and 79.8 ft-lb (108 N·m) oiled, at 75% of proof load. That clamps the joint with 12,771 lbf (56.8 kN).
What torque for a 1/2-13 Grade 5 bolt?
75.4 ft-lb (102 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 1/2-20 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.