Constructed to help evenly spread out airflow from your duct opening, the 801 series butterfly air damper with installation ring is used to cover duct openings in conjunction with a round air diffuser. The design is simple and features high quality steel, brown powder coat finish removable knob control and a plastic key to open and close the damper. Using our product to outfit your ventilation system will improve your home or office air circulation.. Butterfly damper controls airflow into a room. Made of high quality steel. Brown powder coat finish. Removable knob control. Duct opening measurement. Compatible with model# E800-08. Maximum Duct Opening Length (in.): 8. Maximum Duct Opening Width (in.): 8. Installation Location: Wall. Installation Location: Ceiling. Decorative: No