Abstract: A nut assembly for threaded shafts capable of being quickly released from threaded engagement with a shaft, and then moved longitudinally to a selected position on and re-engaged with the shaft. The assembly is characterized by a pair of collar members respectively mounted for relative rotation about fixed parallel axes so as to provide an opening between opposing peripheral segments thereof for receiving the shaft. The inner periphery of one of the members is threaded at the opening and the inner periphery of the other member is provided with a cam surface responsive to said relative rotation for laterally pressing the shaft into threaded engagement with the opposing collar member.