45 degree chamfered on two corners
A square nut having a concave face and a concave or slotted top.
NSN 5910-00-027-3158
NSN 5998-01-038-2440
NSN 5895-01-442-6518
NSN 4140-00-552-7370
NSN 6685-00-052-3293
NSN 5999-01-293-8448
NSN 5996-01-332-8682
NSN 5990-00-548-6163
NSN 6105-00-890-3002
NSN 6135-00-816-9052
NSN 5998-00-872-4257
NSN 6650-01-196-4667