Abstract: A quick-operating locking fastener assembly for use in connecting members together, the fastener assembly comprising a fastener having a threaded shank, and a lock nut assembly receivable on the shank. The lock nut assembly includes a retainer having a passage for receiving the shank, and a seat formed in the retainer. An insert is held in the passage and has internal threads formed thereon for mating with threads of the shank. The insert is radially contractible and expandable between an engaged position in which the insert is threadably engaged with the shank and a disengaged position in which the insert is free to move axially along the shank without engagement of the insert with the shank.