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 6130-00-596-9565
NSN 6320-01-054-3046
NSN 5950-01-477-1553
NSN 6650-01-501-5661
NSN 4140-00-945-4055
NSN 5930-01-386-2042
NSN 6645-01-409-2003
NSN 5910-01-054-9306
NSN 5920-01-391-7624
NSN 5975-01-219-1950
NSN 6320-01-418-2611
NSN 7035-01-509-1959