The specification discloses a locking threaded fastener (10) including a body (12), a coil spring (14), and a compression ring (16). The body is hex-shaped (18) and defines a partially threaded bore (24), an external circumferential groove (32), and a passage (34) extending radially between the bore and the groove. The coil spring is located within the bore and includes a first end (38) angularly fixed with respect to the body and a second end (40) extending through the passage and into the groove. The compression ring is located within the groove and defines an opening (44) receiving the second end of the coil spring. The compression ring is free to move within the groove and includes portions that extending radially outwardly beyond the flats (22) of the hex shape. When a conventional wrench is engaged with the hex shape, the wrench compresses the compression ring to prevent relative angular movement between the ring and the body.