45 degree chamfered on two corners
A square nut having a concave face and a concave or slotted top.
NSN 6130-01-399-6210
NSN 6320-00-433-2773
NSN 5930-01-653-1618
NSN 6240-00-918-2426
NSN 6685-01-373-7979
NSN 6320-00-149-7570
NSN 5910-01-287-4403
NSN 5905-01-155-7657
NSN 5999-01-314-9644
NSN 6610-01-168-1663
NSN 2925-01-294-4125
NSN 5895-01-020-5377