Martyr CMR03AL Aluminum Rudder/Trim Tab Anode with Allen Screw High-quality Martyr anodes are pressure diecast and manufactured to strict quality standards through an ISO 9001 Quality Management System Martyr anodes offer maximum protection by maintaining quality alloys, free from impurities like iron, which can compromise performance Three alloys available - Use Zinc (Martyr I) for salt water, Aluminum (Martyr II) for brackish water, or Magnesium (Martyr III) in fresh water. Use alternative anode alloys when changing water conditions Provides low cost cathodic protection of ocean-going vessels, structures and equipment constructed of iron, steel, aluminum, magnesium, and other metals