Turbine Ventilator Throat Dia 12 in 631 cfm CFM @ 4 MPH Wind Overall Height - Roof Ventilators 17 in Overall Width - Roof Ventilators 19 in Bracing - Roof Ventilators External Construction Material Galvanized Steel With Aluminum Bracing Oiless Bronze Upper Bearing and Lower Thrust Type Ball Bearing Requires Base for New Installations Flashing