Torque Settings

Suggested Starting Values

The below estimated torque calculations are only offered as a guide. Use of its content by anyone is the sole responsibility of that person and they assume all risk. 

The importance of correct bolt tightening cannot be over emphasized.  Determining the correct torque can however present problems.

Approximately 90% of the applied torque is employed in overcoming friction, 50% at the bearing face of the nut and 40% between the mating threads.  It can therefore be seen that only something in the order of 10% effort is employed inducing axial load in the bolt.

Due to many variables that affect the torque-tension relationship like human error, surface texture, and lubrication the only way to determine the correct torque is through experimentation using required lubricants and actual parts under actual joint and assembly conditions.

The torque figures quoted are approximate figures and are available to fasteners in the self-colour condition only.

The figures below do not take into account the effect of plated finishes, special lubricants or the effect of hard and smooth mating surfaces such as hardened washers etc.

The torque figures quoted have been based on a theoretical bolt load equal to 85% of the proof load of the bolting material. Where the proof load is not quoted in the specification this has been taken as 95% of the yield stress.

Metric Bolting

Recommended Tightening Torques Zinc Plated Finish

Select Grade as required below 12.9 / 10.9 / 8.8

NOTES:

( ) Non-Preferred

Zinc Plated co-efficient of friction = 125 (zinc at 8 microns thick).

All torque values are for general guidance.

Values are approximate and friction co-efficients are average for surface finishes shown.

WARNING:

Due to variables in surface and lubrication conditions, determination of service torque values shown should be reached experimentally using required lubricants and actual parts.