M30 bolt torque

An M30 x 3.5 bolt takes 1,515 N·m in class 8.8, 2,095 in 10.9 and 2,449 in 12.9, dry, at 75% of proof load (1117, 1545 and 1806 ft-lb). Fine pitches take a little more. 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
M30 x 3.5coarseClass 4.641956841956831442620928421,282 lbf94.7 kN
Class 8.81,1171,5151,1171,5158381,13655975756,753 lbf252.4 kN
Class 10.91,5452,0951,5452,0951,1591,5727731,04878,508 lbf349.2 kN
Class 12.91,8062,4491,8062,4491,3551,8379031,22491,751 lbf408.1 kN
M30 x 2fineClass 4.646462946462934847223231423,559 lbf104.8 kN
Class 8.81,2371,6771,2371,6779281,25861883862,823 lbf279.4 kN
Class 10.91,7112,3191,7112,3191,2831,7408551,16086,905 lbf386.6 kN
Class 12.91,9992,7111,9992,7111,4992,0331,0001,355101,564 lbf451.8 kN

Work out M30 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%.

M30 x 3.5 Class 8.8, dry, plain steel

1,117ft-lb1,515N·m

040080012001600010002000ft-lbN·m
Clamp load
56,753 lbf (252.4 kN)
Proof load
336.6 kN

The working

  1. Tensile stress area. A = π/4 × (d − 0.9382 × P)² = π/4 × (30 − 0.9382 × 3.5)² = 561 mm²
  2. Proof load. Class 8.8 proof stress is 600 MPa, so A × stress = 336,600 N.
  3. Clamp load. 75% of proof load = 252,450 N.
  4. Torque. T = K × D × F = 0.2 × 30 mm × 252.45 kN = 1,515 N·m (1,117 ft-lb).

Where the M30 x 3.5 numbers come from

The M30 x 3.5 coarse thread has a tensile stress area of 561 mm². A Class 10.9 bolt’s proof stress is 830 MPa, so its proof load is 465,630 N, and 75% of that is a clamp load of 349,223 N.

Torque = K × D × F = 0.20 × 30 mm × 349.22 kN = 2,095 N·m (1,545 ft-lb) dry. With oil (K 0.15) it’s 1,572 N·m (1,159 ft-lb).

Other sizes

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

Questions

What torque for an M30 x 3.5 Class 10.9 bolt?

2,095 N·m (1,545 ft-lb) dry and 1,572 N·m (1,159 ft-lb) oiled, at 75% of proof load. That clamps the joint with 78,508 lbf (349.2 kN).

What torque for an M30 x 3.5 Class 8.8 bolt?

1,515 N·m (1,117 ft-lb) dry, at 75% of proof load; a quarter less with oiled threads.

Coarse or fine thread?

Use whichever the bolt has. The fine M30 x 2 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.