A locking fastener assembly has a fastener with a generally cylindrical body with external threads for assembly with a hollow outer member. Crenellations are provided at a first end of the body for engaging an inner member in the hollow member for preventing rotation of the inner member relative to the locking fastener. At the other end of the body there is a radially extending flange carrying an interrupted annular rim which defines an annular channel between the body and the rim. A locking ring can fit substantially entirely into the annular channel. The ring has a plurality of projections which fit into a plurality of radial slots in the rim for preventing relative rotation between the locking ring and fastener. A snap ring or the like can be used for releasably spacing the locking ring away from the bottom of the annular channel so that the projections on the ring can engage projections on the outer member and prevent relative rotation between the outer member and the split ring.