45 degree chamfered on two corners
A square nut having a concave face and a concave or slotted top.
NSN 6145-00-427-7201
NSN 6220-01-519-2892
NSN 7035-00-368-8761
NSN 5905-01-363-9891
NSN 5990-00-275-7819
NSN 5998-01-100-2428
NSN 5990-01-555-6616
NSN 6685-00-738-2525
NSN 5960-01-278-9394
NSN 5996-00-389-7404
NSN 6105-01-617-9713
NSN 6150-01-218-2425