Broan 433 Automatic Shutter for 353 and 35316 Gable Mount Attic Ventilator N/A Imported Allows more air movement than conventional stationary attic louvers Counter-balanced aluminum vanes open automatically when ventilator is turned on and close when fan stops Flange fits flush against outside wall for neat and smooth appearance Reinforced for strength and provides weather tight closure The frame material is fabricated from.080-6063-T6 extruded aluminum, The louvers are fabricated from.016-3105-H28 aluminum coil For use with Broan models 353 and 35316 attic ventilators Allows more air movement than conventional stationary attic louvers Counter-balanced aluminum vanes open automatically when ventilator is turned on and close when fan stops Flange fits flush against outside wall for neat and smooth appearance Reinforced for strength and provides weather tight closure