Mercury - Fuel Cap Assembly Portable Fuel Tank Components Durable Marine Polymer 8M0060029. Overview. Ask any boater, and they'll tell you that reliability isn't just about the big parts. It's often the small, everyday pieces of equipment that make or break a smooth day on the water. A secure fuel cap gives you that steady confidence that your tank is sealed, protected, and ready for whatever the day brings. The Mercury Fuel Cap Assembly (8M0060029) is one of those quiet essentials - simple, stu