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 5935-01-615-9479
NSN 5920-01-607-6904
NSN 6145-00-900-7081
NSN 5930-01-435-1073
NSN 5999-01-018-7402
NSN 6150-01-536-8966
NSN 5925-01-399-0613
NSN 5990-01-579-2327
NSN 2925-01-305-1370
NSN 5910-00-122-1867
NSN 5950-01-415-9890
NSN 5915-00-244-1702