Abstract: A threaded retainer in the form of a flange head capscrew is used alone or in combination with a large diameter washer to axially, frictionally engage a head of, or block, a threaded fastener so as to prevent the fastener from backing out and becoming loose. Any tendency of the threaded fastener to turn in a loosening direction is resisted by the threaded retainer, in a first embodiment, wherein frictional engagement between the flange head and/or large diameter washer causes the threaded retainer to tend to tighten, and in a second embodiment wherein the flange head and/or large diameter washer cooperates with a recess arrangement in the fastener to block loosening of the fastener.