Abstract: A one-piece spring washer for use with threaded fasteners such as screws has a self-retention feature whereby, once positioned on the screw, it remains firmly in place. The washer comprises an annular body defining a central aperture for receiving the screw shank and a plurality of thread engaging teeth bent up from the body about the aperture for holding the washer in place. Each tooth has a helical thread confronting edge having a pitch that is steeper than, and in the opposite sense of, the pitch of the screw thread so that the teeth extend crosswise of and grip the crest of the thread. A plurality of spring elements are bent up from the washer body outboard of, but in the same direction as, the teeth. The spring elements, which flex downwardly when the screw is tightened against a workpiece, load the screw axially to resist loosening of the screw.