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 2925-01-420-2362
NSN 4140-00-969-3943
NSN 6650-01-468-7704
NSN 5920-01-117-0522
NSN 5935-01-508-4386
NSN 5945-01-430-4992
NSN 5935-00-846-1942
NSN 6130-01-166-5032
NSN 5965-01-038-5994
NSN 5998-01-130-8953
NSN 6645-00-518-2068
NSN 6645-01-563-0441