Bolt torque and preload guide.

Tightening torque is set to reach a target clamp force (preload), commonly 75% of the bolt's proof load. With T = K × F × d, a dry M12 class 8.8 bolt with K = 0.20 needs about 88 N·m for 36.7 kN. Friction changes the answer more than anything else.

Reviewed 11 Nov 2026 · Based on ISO 898-1:2013 (proof stress, stress area); Short-form torque equation T = K·F·d; VDI 2230 for full joint design · Report an error

Questions on this?

88N·m guide torque (65 ft·lbf)
Preload F
36.7 kN
Stress area As
84.3 mm²
Proof stress
580 MPa

T = K × F × d, with F = 75% × proof stress × As. Nut factors are typical values and vary widely with surface condition; for joint design use VDI 2230 or the fastener supplier's tested values.

Guide torque, metric coarse, K = 0.20, preload 75% of proof load (N·m)
Size8.810.912.9Preload 8.8 (kN)
M61115188.8
M825364315.9
M1050728425.2
M128812614736.7
M1414120123550.2
M1621831236568.2
M20441610712110.2
M247611,0531,231158.6
M301,5142,0942,447252.3
Source: Calculated: T = 0.20 × F × d, F = 0.75 × Sp × As, Sp from ISO 898-1 (ISO 898-1:2013 Mechanical properties of fasteners made of carbon steel and alloy steel). Guide values only.

Full torque chart for every finish, M6 to M36

Download the printable chart (PDF)

Reference values, not a design.

Values are the nominal figures of the cited standards, or calculated from them where marked. The governing standard and your drawing always take precedence.

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Questions buyers ask.

What torque should an M12 8.8 bolt be tightened to?

About 88 N·m for a dry, plain or zinc-plated bolt (K = 0.20) at 75% of proof load, which gives about 36.7 kN of preload. A lubricated thread needs less torque for the same preload; follow the value your joint design or equipment maker specifies.

Why does lubrication change the torque?

Most of the applied torque is lost to friction under the head and in the thread. Lubrication lowers the nut factor K, so the same torque produces more preload. Using a dry torque value on an oiled bolt can overload it.

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