# M8 bolt torque

Tighten an M8 × 1.25 class 8.8 bolt to 25 N·m (19 ft-lb) with dry threads, or 19 N·m when lubricated. Class 10.9 takes 36 N·m and class 12.9 takes 43 N·m.

## M8 × 1.25 torque by property class

| Property class | Dry torque (K 0.20) | Lubricated (K 0.15) | Clamp load | Proof load |
|---|---|---|---|---|
| Class 8.8 | 25 N·m (19 ft-lb) | 19 N·m (14 ft-lb) | 15.9 kN | 21.2 kN |
| Class 10.9 | 36 N·m (27 ft-lb) | 27 N·m (20 ft-lb) | 22.8 kN | 30.4 kN |
| Class 12.9 | 43 N·m (31 ft-lb) | 32 N·m (24 ft-lb) | 26.6 kN | 35.5 kN |

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

## M8 bolt data

- Thread: M8 × 1.25 coarse
- Tensile stress area: 36.6 mm²
- Wrench: 13 mm (ISO 4014/4017)
- Socket head cap screw hex key: 6 mm
- Tap drill: 6.8 mm
- Clearance hole (ISO 273): 8.4 close, 9 normal, 10 loose (mm)

## Method

Proof stress from ISO 898-1 (580 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 M8 8.8 bolt?**
About 25 N·m (19 ft-lb) with dry threads and about 19 N·m lubricated, based on 75 % of proof load.

**What is the torque for an M8 10.9 bolt?**
About 36 N·m (27 ft-lb) dry and 27 N·m lubricated.

**What is the torque for an M8 12.9 bolt?**
About 43 N·m (31 ft-lb) dry and 32 N·m lubricated.

**What size wrench fits an M8 bolt?**
13 mm for ISO hex bolts. An M8 socket head cap screw takes a 6 mm hex key.

**What drill size do I need to tap M8?**
Use a 6.8 mm drill for M8 × 1.25 coarse thread.

Source page: https://machinistcharts.com/bolt-torque/m8/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)