Abstract: A damper for register boxes which includes a round damper plate having tab connectors extending from opposite edges, with mount tabs provided on the extending ends of the tab connectors. The damper is designed to locate within the bore of an air duct which is fitted in a register box and the mount tabs are secured to the register box by duct fingers extending from one end of the air duct and folded across the mount tabs. The damper plate is adjustable in the air duct to any selected angle from a position substantially blocking the duct to a position substantially in longitudinal alignment with the duct, by mechanically deforming the tab connectors. A damper and register box apparatus which is characterized by a box frame having an air duct inserted therein. Metal fingers project from the air duct and a damper defined by a damper plate and projecting tab connectors and mount tabs, is fitted in the bore of the air duct and is secured therein by the metal fingers.