M5 bolt torque

An M5 x 0.8 bolt takes 6.2 N·m in class 8.8, 8.8 in 10.9 and 10.3 in 12.9, dry, at 75% of proof load (4.6, 6.5 and 7.6 ft-lb). Oiled threads take a quarter less.

Sources checked

Torque at 75% of proof load.

Units
ThreadClassDryK 0.20Zinc platedK 0.20OiledK 0.15WaxedK 0.10Clamp load
M5 x 0.8coarseClass 4.61.82.41.82.41.31.80.91.2539 lbf2.4 kN
Class 8.84.66.24.66.23.44.62.33.11,389 lbf6.2 kN
Class 10.96.58.86.58.84.96.63.34.41,987 lbf8.8 kN
Class 12.97.610.37.610.35.77.73.85.22,322 lbf10.3 kN

Work out M5 torque

Change grade, threads or preload

Bolt standard

As received, nothing added. K 0.20 (Portland Bolt, Fastenal).

% of proof load

The published charts use 75%.

M5 x 0.8 Class 8.8, dry, plain steel

4.6ft-lb6.2N·m

54.7 in-lb

0102030400204060ft-lbN·m
Clamp load
1,389 lbf (6.2 kN)
Proof load
8.2 kN

The working

  1. Tensile stress area. A = π/4 × (d − 0.9382 × P)² = π/4 × (5 − 0.9382 × 0.8)² = 14.2 mm²
  2. Proof load. Class 8.8 proof stress is 580 MPa, so A × stress = 8,236 N.
  3. Clamp load. 75% of proof load = 6,177 N.
  4. Torque. T = K × D × F = 0.2 × 5 mm × 6.18 kN = 6.2 N·m (4.6 ft-lb).

Where the M5 x 0.8 numbers come from

The M5 x 0.8 coarse thread has a tensile stress area of 14.2 mm². A Class 10.9 bolt’s proof stress is 830 MPa, so its proof load is 11,786 N, and 75% of that is a clamp load of 8,840 N.

Torque = K × D × F = 0.20 × 5 mm × 8.84 kN = 8.8 N·m (6.5 ft-lb) dry. With oil (K 0.15) it’s 6.6 N·m (4.9 ft-lb).

Other sizes

All sizes on one page: the metric bolt torque chart.

Questions

What torque for an M5 x 0.8 Class 10.9 bolt?

8.8 N·m (6.5 ft-lb) dry and 6.6 N·m (4.9 ft-lb) oiled, at 75% of proof load. That clamps the joint with 1,987 lbf (8.8 kN).

What torque for an M5 x 0.8 Class 8.8 bolt?

6.2 N·m (4.6 ft-lb) dry, at 75% of proof load; a quarter less with oiled threads.

Coarse or fine thread?

Use whichever the bolt has. A fine thread has a bigger stress area than the coarse one, so it takes slightly more torque for the same clamp. A thread gauge settles it.

Does this apply to wheel nuts or engine bolts?

No. Use the vehicle maker’s value for those: see lug nut torque by vehicle. These numbers are for general-purpose steel bolts where no spec exists.

Sources

  1. Fastenal: Mechanical properties per ISO 898-1 (externally threaded fasteners): proof stress by property class (checked October 14, 2026)
  2. Engineering Toolbox: Metric bolts: minimum ultimate tensile and proof loads, with ISO 898-1 stress areas (checked October 14, 2026)
  3. Engineering Toolbox: ISO 724 metric threads: coarse and fine pitches with tensile stress areas (checked October 14, 2026)
  4. Engineering Toolbox: Threaded bolts: tensile stress area formulas for unified and ISO metric threads (checked October 14, 2026)
  5. Fastenal: Torque–tension relationship for metric fasteners, property classes 4.6, 8.8, 10.9 and 12.9 (checked October 14, 2026)
  6. Portland Bolt: Bolt torque chart: T = KDP at 75% of proof load, with K for plain, waxed and galvanized bolts (checked October 14, 2026)

Spotted a number that doesn’t match your manual or a source? Tell us; corrections are logged on the sources page.