# M33 bolt torque

Tighten an M33 × 3.5 class 8.8 bolt to 2,060 N·m (1,519 ft-lb) with dry threads, or 1,545 N·m when lubricated. Class 10.9 takes 2,849 N·m and class 12.9 takes 3,330 N·m.

## M33 × 3.5 torque by property class

| Property class | Dry torque (K 0.20) | Lubricated (K 0.15) | Clamp load | Proof load |
|---|---|---|---|---|
| Class 8.8 | 2,060 N·m (1,519 ft-lb) | 1,545 N·m (1,139 ft-lb) | 312.1 kN | 416.1 kN |
| Class 10.9 | 2,849 N·m (2,102 ft-lb) | 2,137 N·m (1,576 ft-lb) | 431.7 kN | 575.6 kN |
| Class 12.9 | 3,330 N·m (2,456 ft-lb) | 2,498 N·m (1,842 ft-lb) | 504.6 kN | 672.7 kN |

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

## M33 bolt data

- Thread: M33 × 3.5 coarse
- Tensile stress area: 693.6 mm²
- Wrench: 50 mm (ISO 4014/4017)
- Socket head cap screw hex key: 24 mm
- Tap drill: 29.5 mm
- Clearance hole (ISO 273): 34 close, 36 normal, 38 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 M33 8.8 bolt?**
About 2,060 N·m (1,519 ft-lb) with dry threads and about 1,545 N·m lubricated, based on 75 % of proof load.

**What is the torque for an M33 10.9 bolt?**
About 2,849 N·m (2,102 ft-lb) dry and 2,137 N·m lubricated.

**What is the torque for an M33 12.9 bolt?**
About 3,330 N·m (2,456 ft-lb) dry and 2,498 N·m lubricated.

**What size wrench fits an M33 bolt?**
50 mm for ISO hex bolts. An M33 socket head cap screw takes a 24 mm hex key.

**What drill size do I need to tap M33?**
Use a 29.5 mm drill for M33 × 3.5 coarse thread.

Source page: https://machinistcharts.com/bolt-torque/m33/
Updated: 2026-10-05
Publisher: MachinistCharts (https://machinistcharts.com)