Built with chrome-plated brass, this clam shell ventilator is a durable and attractive solution to your cabin or below-deck area that requires ventilation. Clam shell vent covers cable pass-through holes, plus shields compartment vent holes and blower exhaust openings to prevent water damage and still permit air flow. Requires #6 screw size. 4" x 3-3/4" base. 2-1/2" wide opening.