Bolt Torque Chart (M6–M24) | Recommended Tightening Torques for 8.8 / 10.9 / Stainless
The most common question on the shop floor: how hard should this bolt be tightened? This chart lists recommended tightening torques for M6-M24 coarse threads in 8.8, 10.9 and A2-70 stainless (dry assembly, mu about 0.14, based on 70% of yield), plus the four factors that shift real torque values and a quick field formula.
Recommended Torques (Coarse Thread, Dry Assembly)
Values assume a friction coefficient of mu about 0.14 (lightly oiled) and 70% yield utilisation. Reference only - critical joints (flanges, pressure vessels, safety parts) must follow the torque stated in the design documents.
| Size | Pitch (mm) | Class 8.8 (N·m) | Class 10.9 (N·m) | A2-70 Stainless (N·m) |
|---|---|---|---|---|
| M6 | 1.0 | 10 | 14 | 7 |
| M8 | 1.25 | 25 | 35 | 17 |
| M10 | 1.5 | 50 | 70 | 33 |
| M12 | 1.75 | 85 | 120 | 58 |
| M14 | 2.0 | 135 | 190 | 93 |
| M16 | 2.0 | 210 | 295 | 145 |
| M20 | 2.5 | 425 | 590 | 290 |
| M24 | 3.0 | 730 | 1000 | 500 |
Four Factors That Shift Real Torque
Lubrication: lubricant lowers friction, so the same torque produces higher preload; dry assembly needs roughly 20-30% more torque for the same preload.
Finish: Dacromet, zinc plate and black oxide each sit at a different friction coefficient (about 0.10-0.20); for high-strength sets, calibrate torque to the same production finish.
Washer and bearing face: flange bolts/nuts have a larger, more stable bearing face and lower torque scatter; a flat washer is more stable than none.
Re-use: repeated install/remove changes thread friction through wear; treat high-strength bolts in critical joints as single-use.
Quick Field Estimation
For emergency estimates use the rule of thumb: T = 0.2 x F x d (T in N·m, F in kN, d = nominal thread diameter in mm).
Preload F is normally taken at 60-75% of the bolt's proof load. Use this for rough checks on non-critical parts only.
For size / grade / friction-condition specific numbers, use the online torque calculator (tools page on this site).
Frequently Asked Questions
No. The values assume mu about 0.14 and 70% yield utilisation and are reference only. Flanges, pressure vessels and safety parts must follow the torque stated in the design documents. When in doubt, send us the duty conditions and our engineers will verify.
A2-70 yields at 450 MPa versus 640 MPa for 8.8, so its usable preload is lower; stainless thread pairs also gall if over-torqued. Hence clearly lower recommended torques for the same size.
Not directly. Lubricant sharply lowers friction, so the same torque creates higher preload and risks over-tightening. Either keep the chart's 'lightly oiled' assumption, or recalculate for the real friction condition (change mu in the torque calculator).
Need specific data from Bolt Torque Chart (M6–M24) | Recommended Tightening Torques for 8.8 / 10.9 / Stainless?
Submit your duty parameters (temperature, pressure, media, speed) — engineers reply with grade selection and quotation within 24 hours.