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Lubricated Bolts and Reduced Torque

Lubrication effect on bolt tension and torque

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When a bolt is lubricated - less torque is required to achieve bolt axial load or tension. Reduction of torques for lubricated vs. dry bolts are indicated in the table below.

LubricantTorque Reduction
(%)
No lube 0
Graphite 50 - 55
White Grease 35 - 45
SAE 30 oil 35 - 45
SAE 40 oil 30 - 40

Example - Reduction of Torque when Bolt is Lubricated

The maximum tightening torque for a slightly lubricated 1" Grade 5 coarse bolt is 483 lb ft. Dry bolt torque is approximately 30% higher - or 628 lb ft.

Tdry = (483 lb ft) (1 + (30%) / (100%))

   = 628 lb ft

If the bolt is lubricated with SAE 30 oil - the torque compared to a dry bolt is reduced with approximately 40%.

TSAE30 = (628 lb ft) (1 - (40%) / (100%))

   = 377 lb ft

Note that if torque specified for a dry or slightly oiled bolt torque is applied to a lubricated bolt  - the bolt may overload and break.

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