Mercury - Quicksilver Trim Tab Anode Corrosion Protection & Steering Aid Cast Aluminum 31640Q4. Overview. Protecting your outboard or sterndrive from corrosion is just as important as keeping it running strong. The Mercury Marine 31640Q4 Quicksilver Aluminum Trim Tab Anode does both - it shields your lower unit from galvanic corrosion and provides subtle steering assistance through its hydrodynamic design. Built for Mercury and Mariner 30-200HP outboards and MerCruiser sterndrives (except Bravo)