The short answer
Tighten a 1/2-13 UNC SAE Grade 8 bolt to about 106 ft·lbf (1,277 in·lbf, 144 N·m) with clean, dry threads. That produces about 12,771 lbf of clamp load, 75% of the bolt's proof load. If the threads are oiled or coated with anti-seize, use less torque. See the table below.
Torque by thread condition and preload (ft·lbf)
| Thread condition | K | 60% proof | 75% proof | 90% proof |
|---|---|---|---|---|
| Dry, plain steel | 0.20 | 85 | 106 | 128 |
| Zinc plated | 0.22 | 94 | 117 | 140 |
| Lightly oiled | 0.15 | 64 | 80 | 96 |
| Anti-seize or moly | 0.12 | 51 | 64 | 77 |
The same torque gives very different clamp loads depending on friction. Torquing a lubricated bolt to a dry-thread value can stretch it past yield.
1/2-13 in other grades (dry, 75% proof)
| Grade | Proof strength | Clamp load (lbf) | Torque (ft·lbf) |
|---|---|---|---|
| Grade 2 | 55 ksi | 5,853 | 49 |
| Grade 5 | 85 ksi | 9,046 | 75 |
| Grade 8 | 120 ksi | 12,771 | 106 |
How it's calculated
When the equipment manufacturer publishes a torque, use theirs. Structural bolts (A325/F3125, A490) are installed by turn-of-nut or tension-control methods under the RCSC specification, not by this chart.
Other Grade 8 sizes
1/4-20 · 5/16-18 · 3/8-16 · 7/16-14 · 9/16-12 · 5/8-11 · 3/4-10 · 7/8-9 · 1-8
Open the full bolt torque calculator with these numbers
Results are estimates for planning and education. Verify against the current code edition your jurisdiction has adopted, manufacturer data and a licensed professional before you build or install.