Martyr CMBRAVO23KITM Magnesium Alloy Merc Bravo 2&3 Mercury Anode Kit  Magnesium Provides low cost cathodic protection of ocean-going vessels, structures and equipment constructed of iron, steel, aluminum, magnesium, and other metals Includes all necessary anodes, hardware and install instructions for easy underwater installation Cathodic protection for Pleasure craft boats Magnesium Alloy for use only in fresh water Only alloy proven to protect in fresh water