Mercury - Rudder Angle Gauge Gray Face 2-1/8" (52 mm) 79-8M0065977. Overview. The Mercury Rudder Angle Gauge (79-8M0065977) lets you see your rudder position instantly, giving you better control and awareness at the helm. It's especially useful when docking, maneuvering in tight spaces, or piloting larger inboard boats. The gray face, bright white numerals, and glass lens provide a clean, modern look that's easy to read in any light. It fits a standard 2-1/8" (52 mm) dash hole and works with Sma