Military Specification MS20002 Series Steel Flat Washer
MS20002 Military Standard washers are high strength, heat-treated washers which must be used with the MS/NAS twelve point and internal wrenching bolts. The chamfer matches the radius under the bolt head. Also good for use with heavy torquing loads where ordinary steel washers would gall.
Note: Although the MS20002 washer will fit over the shanks of standard NAS (1103/1303/6403 etc.) hexbolts, the washer ID is small enough that it will usually "crash" with the bolt head-to-shank radius. DO NOT USE MS20002 WASHERS UNDER THE HEAD OF STANDARD NAS HEX BOLTS.