Triangle Fans Direct-Drive General-Purpose Exhaust Fan - 24in., 1/2 HP Totally enclosed air over (TEAO) thermally protected motor Heavy-gauge galvanized steel fan frame reduces rust and corrosion Built-in shutter opens automatically when fan is turned on and closes when fan is turned off Spiral guard has a polyester powder-coat finish and meets OSHA requirements Built-in shutter with rigid blades for long-lasting, continuous operation