What torque should I use for an M8 8.8 bolt?

A class 8.8 M8 bolt with a coarse thread takes roughly 25 N·m as a guideline at a friction coefficient near 0.14. Always defer to the manufacturer's specification when one exists.

What do bolt property classes like 8.8 and 10.9 mean?

The first number times 100 is the nominal tensile strength in MPa; the second number is ten times the ratio of yield to tensile strength. So 8.8 means about 800 MPa tensile and 640 MPa yield. Higher classes are stronger and take more torque.

Why does the friction coefficient change the torque?

Most of the applied torque is consumed by friction under the bolt head and in the threads. Lubrication lowers friction, so the same torque produces a higher clamp load. Values in this chart assume a typical coefficient around 0.14 for lightly oiled fasteners.

Are these torque values exact?

No. They are general guideline values for standard coarse-thread steel bolts. Actual torque depends on lubrication, surface finish, joint material, washers, and the required clamp load. Use the engineering specification for critical joints.

What units are used in this chart?

Torque is given in newton-metres (N·m). To convert to pound-feet, divide by about 1.356; to kilogram-force metres, divide by about 9.807.

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🔩 Reference

Bolt Torque Chart

Recommended tightening torque for metric bolts (M3–M20) by property class. Pick a size and class to get a target value in N·m.

Size

Property class

Recommended torque — N·m

Torque chart (N·m)

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