Mercury - Trim Gauge Gray Face 2-1/8" (52 mm) 79-8M0065975. Overview. The Mercury Trim Gauge (79-8M0065975) provides a quick, accurate readout of your engine's trim position so you can fine-tune your ride on the water. The clean gray face, crisp white markings, and glass lens make it easy to read in all lighting conditions, and it matches perfectly with Mercury's gray-face gauge family. Designed to fit a standard 2-1/8" (52 mm) dash opening, this gauge integrates directly with SmartCraft systems