Quick-reference torque values for M20 bolts across all property classes. Values shown for dry/plain steel, coarse thread. Click any card for full details including all surface conditions.
These values assume dry/plain steel (K = 0.20) and coarse thread. Oiled, zinc-plated, or lubricated bolts require different torque. See full details →
For a typical M20 class 8.8 bolt the dry figure is 440.6 N·m (325.0 ft·lbs). If the threads are oiled, drop to 330.5 N·m — using the dry number on an oiled bolt would push it about 33% past the intended clamp load. Class 10.9 takes 609.5 N·m, 38% more than 8.8, and the fine M20×1.5 thread raises the 8.8 figure to 488.7 N·m because its stress area is 11% larger.
M20 is structural and heavy-equipment territory. From M18 up, ISO 898-1 raises the class 8.8 proof stress from 580 to 600 MPa, which is why 8.8 figures step up slightly more than the area alone would suggest. Class 9.8 is not defined above M16. At these torques a 3/4" drive wrench or a torque multiplier is usually needed, and the joint is often better controlled by turn-of-nut or direct tension indicators than by torque alone, because a small change in thread friction moves the clamp load by thousands of newtons.
N·m. Coarse thread unless noted. Clamp load is the 75%-of-proof preload the torque is sized to produce.
| Coarse thread | M20×2.5 |
| Fine thread | M20×1.5 |
| Stress area (coarse / fine) | 244.79 / 271.5 mm² |
| Hex wrench size | 30 mm (ISO 4032) |
| Tap drill (coarse / fine) | 17.5 mm / 18.5 mm |
| Clearance hole (ISO 273 medium) | 22 mm |
Pitches per ISO 261/262; stress area per ISO 898-1; tap drill = nominal diameter minus pitch. M20 coarse vs fine →