Cover height adjuster

A cover height adjuster assembly comprising a lower ring, an upper ring vertically above the lower ring and having a skirt surrounding the lower ring;

• the lower ring having an upwardly castellated upper surface and the upper ring having a downwardly castellated lower surface within said skirt complementary to said upwardly castellated surface and being supported thereby, one of said castellated surfaces comprising horizontal steps separated by notches defined by notch surfaces and the other of said castellated surfaces comprising horizontal steps separated by projections at last some of which are positionable in respective said notches and inhibited by the notch surfaces thereof against relative rotation of the rings when so positioned, said castellated upper and lower surfaces generally sloping around at least three sectors of said lower and upper rings, respectively, such that the height of said upper ring with respect to said lower ring varies with different relative rotational positions of said upper and lower rings, said upper ring having a sloping upper surface;
• and
• a cover support ring surmounting said upper ring and having an upper surface and a lower surface which slopes with respect to said cover support ring upper surface and which abuts said sloping upper ring upper surface, such that said cover support ring upper surface has a slope which varies with relative rotational positions of said cover support ring and upper ring.