A washer or cone or disk shape with a centrally located hole, designed to accommodate a flat or oval head screw and provide additional bearing area on the material being fastened. It may or may not have a flush flange feature.
NSN 6620-01-277-9325
NSN 4140-01-515-1121
NSN 4140-01-435-6198
NSN 5905-01-513-7532
NSN 5945-01-401-5323
NSN 6145-01-634-0388
NSN 5855-01-430-3246
NSN 5895-01-200-1688
NSN 5935-01-518-0458
NSN 5895-00-417-3215
NSN 6135-01-421-7168
NSN 5965-01-479-9155