24 in Backdraft Damper / Wall Shutter, 24 1/2 in x 24 1/2 in Opening Required/ SPECIAL FEATURES: VENTILLATION LOUVER,SINGLE PANELSHUTTER,ALUMINUM VANES,STEEL PIVOT PINS,19 GAUGE STEEL FRAME,3" DEEP 1 5/8 IN. FLANGE,24 INCH INSIDE OPENING,GRAY ENAMEL FINISH,DESIGNED FOR MOTOR OPERATOR DAYTON MODEL 1C746,P/OA MODIFICATION TO ELEMINATE ASR-8 FAILURES CAUSED BY OVERHEAT DUE TO AIR LEAKAGE THROUGH EXISTING VENTILATION