Model 155B duct ring with butterfly damper combination for use with round ceiling diffuser model 150W. This item allows you to add air volume control to your diffuser. All-steel construction, brown finish. This also enables the diffuser to be either surface mounted or mounted directly to exposed ductwork. The damper has a plastic T-handle operator that is inserted through the center of the 150W diffuser. It may be left installed in the diffuser or removed after each use. Note if you order this damper you do not order the 156R ring as well as it is already included!