Mercury - Water Level Gauge Black Face 2-1/8" (52 mm) 79-8M0052846. Overview. The Mercury Water Level Gauge (79-8M0052846) gives you a quick, accurate view of your freshwater or livewell tank levels. It features a black face, crisp white markings, and a glass lens for clear visibility in any light. The gauge fits a standard 2-1/8" (52 mm) dash opening and works with SmartCraft-compatible systems when water-level sensors are installed. It's durable, easy to read, and designed to blend perfectly w