45 degree chamfered on two corners
A square nut having a concave face and a concave or slotted top.
NSN 4140-01-384-3930
NSN 5855-01-557-1798
NSN 5855-01-586-9232
NSN 6110-01-357-7749
NSN 6650-01-381-1432
NSN 6150-00-729-9420
NSN 6135-01-106-7740
NSN 5920-00-694-0483
NSN 6620-01-462-0001
NSN 5925-00-364-7969
NSN 5999-01-598-5666
NSN 5960-01-157-7009