Martyr CM55989Z, Zinc Alloy Button Mercury/Mercruiser Anode Provides low cost cathodic protection of ocean-going vessels, structures and equipment constructed of iron, steel, aluminum, magnesium, and other metals Zinc Alloy for use in saltwater Cathodic protection for Pleasure craft boats Not recommended for use in fresh water High-quality Martyr anodes are pressure diecast and manufactured to strict quality standards through an ISO 9001 Quality Management System