Locking fastener

In a locking threaded fastener of the type comprising a threaded shank with threads advancing axially of the shank in a tightening direction from an outer end to an inner end, and a nut assemblage including a first nut member having a through-hole for a clearance fit with the threaded shank and including a second nut member with a threaded hole for threaded engagement with the threaded shank, the second nut member being disposed nearer the outer end of the threaded shank than the first nut member whereby a workpiece surface may be disposed between the first nut member and the inner end of the threaded shank, said nut assemblage also including means for coupling the first and second nut members together for rotation together when the second nut member is rotated in the tightening direction and wedge means for wedging the first and second nut member axially apart in response to rotation of the second nut member relative to the shank in the loosening direction, the wedge means having a wedge angle which is greater than the angle of the threads whereby such rotation causes the threads to jam and inhibit loosening of the second nut member, the improvement in said nut assemblage including:

• a third nut member having a through-hole for a clearance fit with said threaded shank and being disposed with the first nut member between it and the second nut member,
• a flat inner surface on the third nut member for engaging the workpiece,
• a flat outer surface on the third nut member and a flat inner surface on the first nut member for engagement with the flat outer surface on the third nut member,
• said wedge means having engaging surfaces with a coefficient of friction less than the coefficient of friction between the flat outer surface on the third nut member and the flat inner surface on the first nut member, the last mentioned coefficient being less than that between the flat inner surface of the third nut and workpiece.