Mercury - Gauge Seal 85 mm Fits SmartCraft System Gauges 12-859656. Overview. The Mercury Gauge Seal (12-859656) keeps your larger 3-3/8" (85 mm) SmartCraft System Link gauges sealed tight against water and debris. This OEM rubber seal fits between the gauge and dash, creating a weatherproof barrier that prevents leaks and protects your electronics from damage caused by moisture, vibration, or corrosion.. Built from durable, marine-grade rubber, this seal stays flexible and strong through years