Wind-Driven Turbine Exhaust Ventilator, Bracing Location External, Head Diameter 16 1/4 in, Throat Diameter 10 in, Airflow @ 4 mph 425 cfm, Metal Material Thickness 24 ga, 26 ga, Overall Height 16 1/4 in, Overall Width 16 1/4 in, Housing Material Steel, Bearing Type Lower Thrust Ball Bearing, Oilless Bronze Upper Bearing, Bracing Material Aluminum, Housing Finish Galvanized, Includes -, Installation Requirements Base for New Installations, Flashing Wind-driven turbine ventilator is externally braced for strength and perfect alignment. It is designed with a bronze, oil-impregnated top bearing. Vents have a bottom thrust-type pivot bearing with a hardened steel ball riding in a hardended steel seat.