Abstract: A mounting shoulder (34) attached to an air duct fitting (20) for securing an air duct register (24) over the end of the fitting. The fitting protrudes through an opening (26) in a wall member (22). The mounting shoulder comprises an attachment strip (36), a floor plate (32), and three side walls (40, 42, 44) all formed from a single plate of metal having properly placed cuts and bends. The attachment strip (36) affixes the shoulder to the fitting and is attached to the fitting such that its lower edge (52) is flush with the lower edge of the fitting. The width of the attachment strip is substantially equal to the thickness of the wall member. The floor plate, to which the air duct register may be secured, is attached along one edge to the attachment strip and lies in a plane substantially parallel to the wall member. The three side walls extend in a direction away from wall member from edges of the floor plate.