Mercury - Quicksilver 821630A2 Magnesium Anode Assembly MerCruiser Bravo, X, XR & XZ Drives Freshwater Use 821630A2. Overview. Freshwater boating brings its own kind of corrosion, and magnesium is your best defense against it. The Quicksilver 821630A2 Magnesium Anode Assembly protects your MerCruiser Bravo, X, XR, and XZ drives from galvanic corrosion - the kind of hidden damage that can quietly eat away at your sterndrive's metal components.. Made from high-purity magnesium, this OEM anode is e