A threaded fastener having a two-piece nut member (20) and a bolt (15) with the nut member (20) having a threaded nut member (35) and a base member (30) is disclosed. The threaded nut member (35) has a body portion (70) and a neck portion (65), the fleck portion (65) engaging with a transition beginning engagement on the base member (30). The base member (30) includes a transition portion (50), the diameter of the transition portion (50) increasing radially as it extends axially from the cylindrical through bore portion (55) to an increased diameter at the outer planar surface of the base member. Movement of the neck potion (65) into the base member (30) resuits in the threaded form (75) having a compressive engagement with engaged threads (135) of the bolt (15) to provicle the prevailing torque structure. The threaded nut member (35) and base member (30) may be made of dissimilar materials and are more flexible in use with varying bearing surfaces.
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