Mercury - Gear Oil Pressure Gauge 600 PSI Dual Scale White Face 2-1/8" (52 mm) 79-8M0069415. Overview. The Mercury Gear Oil Pressure Gauge (79-8M0069415) lets you keep an eye on your gearcase health with precision. It displays oil pressure up to 600 PSI and features a dual-scale face showing both PSI and Bar for easy reading in either English or Metric units. With its white face, crisp black markings, and glass lens, it matches the rest of your Mercury OEM gauges perfectly. Built to fit a standa