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ses 75% of the yield strength. The prevailing torque lock nut clamp loads are listed at 75% of the proof loads specified for the appropriate grade bolt: Grade C – SAE J429 Grade 8, FNL Grade 9 – FNL Grade 9 bolt, Grade F – SAE J429 Grade 5.
The bolt is stressed up to the proofload value, and if there is no deformation, elongation, or fracture, then the bolt is deemed to have passed. For bolting specifications that do not have a published proofload, it is usually calculated at 92% of minimum yield strength.
Because there are many variables that affect the torque-tension relationship, the only way to determine the correct torque is through experimentation under actual joint and assembly conditions. Bolt torque chart reference guides include Grade 2, B7, A307, A325, Grade 8, A490, and Grade 5.
Torque Table. The following suggested tightening torques provide an excellent starting point for determining torque requirements. Remember, you may need to vary these numbers somewhat based on the individual joint or the amount of fastener lubrication.
U.S. Recommended Bolt Torque Table. * Sizes from 4 to 10 are in in.-lbs. Sizes from 1/4 up are in ft.-lbs. ** Fine thread figures are for 1-14. Grade 2, 5, and 8 values are for plated bolts.
The charts below show the ideal tightening torque for each bolt grade for a variety of sizes. The size column also includes the thread count. Identify the grade, size, and thread density of your bolts and refer to the tightening torque columns.
Torque specifications, especially for critical joints, should be determined under actual assembly conditions due to the many variables involved which are difficult to predict and do affect the torque-tension relationship. The above recommended clamp loads are based on 75% of the minimum specified proof loads for each grade and size. Proof. Tensile.
