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M22 bolt tightening torque

A M22 bolt in Class 10.9, dry, torques to about 831 N·m (613 lb-ft) at 75% of proof load.

22 mm major dia · 2.5 mm pitch · At = 303 mm² · clean, undamaged threads

Torque calculator T = K·D·F
Tightening torque
Tightening torque
T=K⋅D⋅FT = K \cdot D \cdot F
T torque · K nut factor (friction) · D nominal diameter · F preload
Preload (target clamp load)
F=u⋅Sp⋅AtF = u \cdot S_p \cdot A_t
u utilisation (0.75) · Sp proof strength · At tensile stress area

M22 torque by grade and lubrication (N·m)

GradeDry / as-received steel
K=0.2		Zinc plated
K=0.22		Lubricated (light oil)
K=0.15		Molybdenum disulfide
K=0.1		Anti-seize compound
K=0.13		Waxed / PTFE
K=0.1
Class 8.8601661451300390300
Class 10.9831914623416540416
Class 12.99711070728486631486
A2-70 Stainless451496338225293225

Proof strengths per ISO 898-1 (ISO 3506-1 for A2-70); tensile stress area per ISO 898-1. Values at 75 % of proof load.

Caution — match the column to your assembly. The same bolt can need half the torque lubricated versus dry, because K drops from ~0.20 to ~0.10. A dry-torque figure applied to a lubricated bolt over-tightens it and can snap it.

How the value is worked out

Torque isn't the goal — clamp load is. Tightening stretches the bolt into a controlled tension that squeezes the joint together. For a M22 in Class 12.9 at 75 % of proof load that target tension is about 221 kN; torque is just the indirect lever used to reach it, and the relationship runs through the nut factor K. The tensile stress area of the M22 thread is 303 mm²; multiply it by the grade's proof strength and by 0.75 to get the preload F, then feed F into T = K·D·F for the table above.

Choosing the right friction condition

This is the input people get wrong most often. K bundles every friction loss in the joint — under the head and across the threads — and it moves the torque dramatically: dry, a M22 in Class 12.9 wants about 971 N·m; with light oil only 728 N·m; with MoS₂ roughly 486 N·m — for the same target tension. Always match the column to what is actually on the threads.

Grade matters as much as size

Class 8.8 tolerates roughly 601 N·m dry; Class 12.9 in the same diameter takes about 971 N·m because it safely holds far more tension. Torquing a lower grade to a higher grade's table is another classic way to fail a joint — check the head markings before picking a row. And remember: torque-wrench control scatters ±25 % in practice; for safety-critical joints use angle-control or direct tension measurement.

Tapping the mating hole? M22 tap drill size  ·  M22 clearance hole

References

  1. ISO 898-1 — Mechanical properties of fasteners: property classes 8.8 / 10.9 / 12.9 (ISO 3506-1 for A2-70).
  2. ISO 724 / ISO 898-1 — metric thread dimensions and tensile stress area.
  3. Machinery’s Handbook — torque–preload relation and nut-factor scatter.

Last reviewed: 2026-07 · Calculation method & assumptions