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 6620-01-104-5758
NSN 5925-01-634-0664
NSN 6320-01-313-2709
NSN 5960-01-541-5734
NSN 6685-01-543-8220
NSN 5920-00-003-2940
NSN 5855-01-432-0524
NSN 6620-00-787-6683
NSN 6110-01-478-9941
NSN 6105-01-407-8697
NSN 6620-00-104-6937
NSN 6135-01-048-0910