# M18 bolt torque

Tighten an M18 × 2.5 class 8.8 bolt to 312 N·m (230 ft-lb) with dry threads, or 234 N·m when lubricated. Class 10.9 takes 431 N·m and class 12.9 takes 504 N·m.

## M18 × 2.5 torque by property class

| Property class | Dry torque (K 0.20) | Lubricated (K 0.15) | Clamp load | Proof load |
|---|---|---|---|---|
| Class 8.8 | 312 N·m (230 ft-lb) | 234 N·m (172 ft-lb) | 86.6 kN | 115.5 kN |
| Class 10.9 | 431 N·m (318 ft-lb) | 323 N·m (239 ft-lb) | 119.8 kN | 159.8 kN |
| Class 12.9 | 504 N·m (372 ft-lb) | 378 N·m (279 ft-lb) | 140.0 kN | 186.7 kN |

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

## M18 bolt data

- Thread: M18 × 2.5 coarse
- Tensile stress area: 192.5 mm²
- Wrench: 27 mm (ISO 4014/4017)
- Socket head cap screw hex key: 14 mm
- Tap drill: 15.5 mm
- Clearance hole (ISO 273): 19 close, 20 normal, 21 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 M18 8.8 bolt?**
About 312 N·m (230 ft-lb) with dry threads and about 234 N·m lubricated, based on 75 % of proof load.

**What is the torque for an M18 10.9 bolt?**
About 431 N·m (318 ft-lb) dry and 323 N·m lubricated.

**What is the torque for an M18 12.9 bolt?**
About 504 N·m (372 ft-lb) dry and 378 N·m lubricated.

**What size wrench fits an M18 bolt?**
27 mm for ISO hex bolts. An M18 socket head cap screw takes a 14 mm hex key.

**What drill size do I need to tap M18?**
Use a 15.5 mm drill for M18 × 2.5 coarse thread.

Source page: https://machinistcharts.com/bolt-torque/m18/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)