Bolt torque chart for SAE grades
These are dry, plain-finish values in foot-pounds, calculated at 75 percent of proof load with a nut factor of 0.20. Multiply by 0.75 for oiled or waxed threads, and by about 0.85 for zinc plated.
Grade is marked on the head. Grade 2 has no marks, grade 5 has three radial lines, grade 8 has six.
| Size | Grade 2 | Grade 5 | Grade 8 |
|---|---|---|---|
| 1/4-20 | 5 | 8 | 12 |
| 5/16-18 | 11 | 17 | 25 |
| 3/8-16 | 20 | 30 | 45 |
| 7/16-14 | 32 | 50 | 70 |
| 1/2-13 | 49 | 75 | 110 |
| 9/16-12 | 70 | 110 | 150 |
| 5/8-11 | 97 | 150 | 220 |
| 3/4-10 | 172 | 265 | 380 |
| 7/8-9 | 160 | 420 | 600 |
| 1-8 | 240 | 640 | 900 |
Bolt torque calculator
The working formula is T = K x D x P, where T is torque, K is the nut factor, D is nominal diameter and P is the target clamp load. Use K = 0.20 dry, 0.15 lubricated and 0.17 for zinc plated.
- Torque
- 75 ft-lb / 102 Nm
Target clamp load 9,046 lb at 75 percent of proof, nut factor 0.2. Where the equipment manufacturer publishes a figure, use theirs instead.
Torque sequence and pattern
On any joint with a gasket or a machined face, tighten in a criss-cross star pattern in at least three passes: 30 percent of final torque, then 60, then 100. Going straight to full torque on the first pass pulls the joint out of flat and the first bolts you tightened end up loose.
On a circular flange, work across the diameter each time rather than round the circle. On a rectangular cover, start in the middle and spiral outward.
Torque specs for U bolts
U bolts have two threaded legs sharing one load, so tighten them alternately in small increments rather than one leg at a time. Uneven tightening bends the bolt and the joint never seats.
Where the manufacturer gives a figure, use it. U bolts on leaf spring and axle work are usually specified as a stretch or a re-torque interval rather than a single number, because they relax after the first load cycles. Re-torque after the first run.
