Frost King Winterrized Plastic Turbine Vent Cover, Fits average size Fits over roof ventilator Helps prevent heat from escaping Easy to use and install Durable for use Easy simple instructions Turbine Vent Cover Prevents Heat From Escaping Through Vent Elastic With Tie Cords Fits The Average 22-Inch Diameter X 15-Inch Vents Made From Durable, Black Polyethylene