A rail-carrying plate lies on an upper surface of a base. An anchor-bolt assembly has an elastomeric buffer sheet between the rail plate and the base upper surface and a bolt set in the anchor sleeve passing through the rail plate. An inner ring surrounds the bolt, bears directly on the base surface, is pressed downward by the bolt against the base surface, has an annular outwardly directed outer surface. An outer ring is transfixed by the bolt, has an annular inner surface spaced outward from the inner-ring outer surface, and bears upward on the rail plate. An annular elastomeric body between the inner and outer rings is bonded to the respective outer and inner surfaces thereof so that vertical displacement of the outer ring relative to the inner ring tends to self-center the two rings.