# M20 bolt torque

Tighten an M20 × 2.5 class 8.8 bolt to 441 N·m (325 ft-lb) with dry threads, or 330 N·m when lubricated. Class 10.9 takes 610 N·m and class 12.9 takes 712 N·m.

## M20 × 2.5 torque by property class

| Property class | Dry torque (K 0.20) | Lubricated (K 0.15) | Clamp load | Proof load |
|---|---|---|---|---|
| Class 8.8 | 441 N·m (325 ft-lb) | 330 N·m (244 ft-lb) | 110.2 kN | 146.9 kN |
| Class 10.9 | 610 N·m (450 ft-lb) | 457 N·m (337 ft-lb) | 152.4 kN | 203.2 kN |
| Class 12.9 | 712 N·m (525 ft-lb) | 534 N·m (394 ft-lb) | 178.1 kN | 237.5 kN |

Clamp load = 75 % of proof load. Method: T = K × F × d.

## M20 bolt data

- Thread: M20 × 2.5 coarse
- Tensile stress area: 244.8 mm²
- Wrench: 30 mm (ISO 4014/4017)
- Socket head cap screw hex key: 17 mm
- Tap drill: 17.5 mm
- Clearance hole (ISO 273): 21 close, 22 normal, 24 loose (mm)

## Method

Proof stress from ISO 898-1 (600 MPa for 8.8 at this size, 830 MPa for 10.9, 970 MPa for 12.9) × tensile stress area As = π/4 × (d − 0.9382 p)². Target clamp load F = 75 % of proof load. T = K × F × d with K = 0.20 dry, 0.15 lubricated.

## FAQ

**What is the torque for an M20 8.8 bolt?**
About 441 N·m (325 ft-lb) with dry threads and about 330 N·m lubricated, based on 75 % of proof load.

**What is the torque for an M20 10.9 bolt?**
About 610 N·m (450 ft-lb) dry and 457 N·m lubricated.

**What is the torque for an M20 12.9 bolt?**
About 712 N·m (525 ft-lb) dry and 534 N·m lubricated.

**What size wrench fits an M20 bolt?**
30 mm for ISO hex bolts. An M20 socket head cap screw takes a 17 mm hex key.

**What drill size do I need to tap M20?**
Use a 17.5 mm drill for M20 × 2.5 coarse thread.

Source page: https://machinistcharts.com/bolt-torque/m20/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)