Torque & Preload Quick Reference
Tightening torque sets the preload: too loose and the joint shakes loose; too tight and the bolt snaps. The table below lists common reference torques for dry, metric coarse threads (K≈0.2) — always confirm against your actual process and materials.
| Thread | 8.8 gr (N·m) | 10.9 gr (N·m) | 12.9 gr (N·m) |
|---|---|---|---|
| M5 | 4.9 | 7.2 | 8.5 |
| M6 | 8.4 | 12.4 | 14.6 |
| M8 | 20 | 30 | 35 |
| M10 | 40 | 58 | 69 |
| M12 | 70 | 102 | 120 |
| M16 | 170 | 245 | 290 |
| M20 | 330 | 480 | 565 |
| M24 | 570 | 830 | 975 |
Tightening Tips
- Lubrication lowers torque: oiled or coated threads reduce friction — reduce torque by 20–30% or you will over-tighten.
- Stainless galls easily: tighten 304 / 316 slowly with lubricant to avoid thread cold-welding / galling.
- Locking parts cost torque: nylon-insert lock nuts consume roughly 15–25% more torque than plain nuts.
- Tighten in steps, criss-cross: for flanges and covers, torque in 2–3 passes on a diagonal pattern to avoid uneven loading.
- Calibrate your wrench: use a settable torque wrench and keep it calibrated for high-strength bolts.
Preload is normally taken at 70–80% of yield strength. For the theory and 8.8 / 10.9 / 12.9 comparison, read High-strength bolt torque guide.