USCG certified for use on sail or power driven vessels under 20 meters (65.6 ft.) in length. 3-mile visibility. Black plastic and chrome plated zinc alloy top, chrome plated brass base (3-3/8″ x 2-1/4″) with waterproof cover. Stowaway plug-in type with 3/4″ diameter anodized aluminum tube & gold plated contacts. Deck mount. Clear lenses. 12V bulbs included. Screw size is 8.