Mercury - SC1000 Tachometer 4000 RPM SmartCraft Analog Gauge Gray Face 85 mm 79-8M0135644. Overview. The Mercury SC1000 4000 RPM Tachometer (79-8M0135644) delivers reliable, real-time engine data with a clean, gray-face design that gives any dash a modern look. It fits a standard 85 mm (3-3/8 in.) gauge opening and connects directly to your SmartCraft network for smooth, accurate RPM readings. Built tough for marine conditions, it's easy to read, simple to install, and fully compatible with Smar