Short answer: use the application’s tightening torque (based on bolt size, grade, lubrication, and desired clamp load) and verify that the nut’s prevailing torque is within the limits of ISO 2320. The table below shows prevailing-torque ranges for Auto-Lok nuts (Class 8 and Class 10).
Tip: Tightening (installation) torque creates clamp load; prevailing torque is the extra torsional resistance from the nut’s locking feature. They are not the same value.
| NF EN ISO 2320 | “ALNS(h)” and “ALND” CL.8 | “ALNS(h)” and “ALND” CL.10 | ||||||
|---|---|---|---|---|---|---|---|---|
| Tension (Bolt in kN) | Locking torque (N·m) | Tension (Bolt in kN) | Locking torque (N·m) | |||||
| Standard threads | on the | 1st turn MAX | 1st deturn MIN | 5th deturn MIN | on the | 1st turn MAX | 1st deturn MIN | 5th deturn MIN |
| M3×0,5 | 2,2 | 0,43 | 0,12 | 0,08 | 3,1 | 0,60 | 0,15 | 0,10 |
| M4×0,7 | 3,8 | 0,90 | 0,18 | 0,12 | 5,5 | 1,20 | 0,22 | 0,15 |
| M5×0,8 | 6,2 | 1,60 | 0,29 | 0,20 | 8,9 | 2,10 | 0,35 | 0,24 |
| M6×1 | 8,7 | 3,00 | 0,45 | 0,30 | 12,5 | 4,00 | 0,55 | 0,40 |
| M8×1,25 | 15,9 | 6,00 | 0,85 | 0,60 | 22,8 | 8,00 | 1,15 | 0,80 |
| M10×1,5 | 25,3 | 10,50 | 1,50 | 1,00 | 36,1 | 14,00 | 2,00 | 1,40 |
| M12×1,75 | 36,7 | 15,50 | 2,30 | 1,60 | 52,5 | 21,00 | 3,10 | 2,10 |
| M14×2 | 50 | 24,00 | 3,30 | 2,30 | 71,6 | 31,00 | 4,40 | 3,00 |
| M16×2 | 68,2 | 32,00 | 4,50 | 3,00 | 97,5 | 42,00 | 6,00 | 4,20 |
| M18×2,5 | 86,2 | 42,00 | 6,00 | 4,20 | 119 | 56,00 | 8,00 | 5,50 |
| M20×2,5 | 110 | 54,00 | 7,50 | 5,30 | 152 | 72,00 | 10,50 | 7,00 |
| M22×2,5 | 136 | 68,00 | 9,50 | 6,50 | 189 | 90,00 | 13,00 | 9,00 |
| M24×3 | 159 | 80,00 | 11,50 | 8,00 | 220 | 106,00 | 15,00 | 10,50 |
| M27×3 | 206 | 94,00 | 13,50 | 10,00 | 286 | 123,00 | 17,00 | 12,00 |
| M30×3,5 | 253 | 108,00 | 16,00 | 12,00 | 350 | 140,00 | 19,00 | 14,00 |
| Fine threads | Tension (Bolt in kN) | Locking torque (N·m) | Tension (Bolt in kN) | Locking torque (N·m) | ||||
| On the | 1st turn MAX | 1st deturn MIN | 5th deturn MIN | on the | 1st turn MAX | 1st deturn MIN | 5th deturn MIN | |
| M8×1 | 17 | 6,00 | 0,85 | 0,60 | 24,4 | 8,00 | 1,15 | 0,80 |
| M10×1 | 28,1 | 10,50 | 1,50 | 1,00 | 40,1 | 14,00 | 2,00 | 1,40 |
| M10×1,25 | 26,6 | 10,50 | 1,50 | 1,00 | 38,1 | 14,00 | 2,00 | 1,40 |
| M12×1,25 | 41 | 15,50 | 2,30 | 1,60 | 57,3 | 21,00 | 3,10 | 2,10 |
| M12×1,50 | 38,3 | 15,50 | 2,30 | 1,60 | 54,8 | 21,00 | 3,10 | 2,10 |
| M14×1,50 | 54,4 | 24,00 | 3,30 | 2,30 | 78 | 31,00 | 4,40 | 3,00 |
| M16×1,5 | 72,7 | 32,00 | 4,50 | 3,00 | 104 | 46,00 | 6,00 | 4,20 |
| M18×1,5 | 97,5 | 42,00 | 6,00 | 4,20 | 134 | 56,00 | 8,00 | 5,50 |
| M20×1,5 | 122 | 54,00 | 7,50 | 5,30 | 169 | 72,00 | 10,50 | 7,00 |
| M22×1,5 | 150 | 68,00 | 9,50 | 6,50 | 207 | 90,00 | 13,00 | 9,00 |
| M24×2 | 173 | 80,00 | 11,50 | 8,00 | 239 | 106,00 | 15,00 | 10,50 |
| M27×2 | 224 | 94,00 | 13,50 | 10,00 | 309 | 123,00 | 17,00 | 12,00 |
| M30×2 | 280 | 108,00 | 16,00 | 12,00 | 386 | 140,00 | 19,00 | 14,00 |
How to pick your tightening torque (quick method)
- Identify bolt size and grade (e.g., M8, property class 8.8 or 10.9), and whether threads are dry or lubricated.
- Find the target clamp load (F) for your joint. A typical design uses 70–80% of bolt proof load.
- Estimate tightening torque with a standard relation:
T ≈ K × F × d(K ≈ 0.18–0.25 dry; ≈0.12–0.18 lubricated). This is your installation torque. - Verify prevailing torque in the table: the nut’s locking resistance should sit within ISO 2320 limits across cycles (1st turn, 1st and 5th removal).
For flight-critical assemblies, always validate against your spec and perform joint testing. Prevailing torque values above include only the locking feature; they do not replace your joint’s tightening torque.