The short answer
Tighten a 3/8-16 UNC SAE Grade 8 bolt to about 44 ft·lbf (523 in·lbf, 59 N·m) with clean, dry threads. That produces about 6,974 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 | 35 | 44 | 52 |
| Zinc plated | 0.22 | 38 | 48 | 58 |
| Lightly oiled | 0.15 | 26 | 33 | 39 |
| Anti-seize or moly | 0.12 | 21 | 26 | 31 |
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.
3/8-16 in other grades (dry, 75% proof)
| Grade | Proof strength | Clamp load (lbf) | Torque (ft·lbf) |
|---|---|---|---|
| Grade 2 | 55 ksi | 3,196 | 20 |
| Grade 5 | 85 ksi | 4,940 | 31 |
| Grade 8 | 120 ksi | 6,974 | 44 |
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 · 7/16-14 · 1/2-13 · 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.