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 5835-00-498-1551
NSN 5960-01-389-4055
NSN 7035-01-211-5636
NSN 5935-01-285-4419
NSN 5915-00-553-8755
NSN 6620-01-125-0794
NSN 6130-01-142-1308
NSN 6145-01-422-9505
NSN 5925-00-072-9933
NSN 6130-01-358-4943
NSN 5999-01-381-5510
NSN 6650-00-514-3531