Mercury Aluminum Trim Tab Anode Kit | Canada Metals CM31640KITA Mercury Aluminum Trim Tab Anode Kit | Martyr CM31640KITA Premium aluminum Martyr anode is designed to protect a gearcase from corrosion in salt or brackish water. Mercury trim tab anode kit Aluminum anode for use in brackish and salt water applications Kit includes mounting bolt Aluminum replacement for Mercury's zinc anode p/n 31640Q4 For freshwater use magnesium anode p/n CM31640KITM