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 6135-01-642-0733
NSN 5950-01-196-6317
NSN 5960-00-372-4876
NSN 5999-01-493-3185
NSN 6320-00-004-9158
NSN 5950-01-417-2883
NSN 6130-01-167-7526
NSN 6650-01-267-6522
NSN 6620-01-271-0711
NSN 5950-01-488-9848
NSN 6650-00-170-5095
NSN 4140-01-033-4953