A fitting has a threaded insert to be tightened within a housing bore. A first lock ring has an anti-rotation structure on an outer peripheral surface to interfit with anti-rotation structure in a housing. The first lock ring has a face extending generally perpendicular to an axis of the insert, with anti-rotation structure included on the first face. A second lock ring has anti-rotation structure on a face which extends perpendicular to an axis of the threaded insert. The anti-rotation structure on the faces of the first and second lock ring interfit to resist relative rotation of the two. An assembly is also disclosed.