INTERN ESP B-4.101-GS PDF

GENERAL: A prevailing-torque bolt is one which is torsionally resistant to rotation due to a self-contained prevailing- torque feature and not because of a compressive load developed against the under head bearing surface, a tensile load developed in the shank, or frictional devices designed into the underside of the head. These latter types normally are considered "free running" locking bolts and have high breakaway torsion requirements but no prevailing-torque. A prevailing-torque bolt intends to delay or prevent total disassembly of joint when clamp force is decreased or ceases to exist.

The threaded fasteners covered by this standard are prevailing-torque hexagon head bolts with a non-metallic plastic patch bonded to a specified portion of the threads to provide the prevailing-torque feature. These bolts are for applications where temperatures will not exceed 250 F. All mating tapped holes should be countersunk before threading. Included angle of countersinks should be 90 degrees and the diameter of countersinks should be .030 inch larger than the nominal diameter of the thread for 1/4 inch size up to .040 inch to .050 inch over nominal for larger sizes.