Martyr magnesium trim cylinder anode protects trim cylinder from corrosion in fresh water lakes and rivers. Mercury Magnesium Trim Cylinder Anode | Martyr CM806189M Mercruiser trim cylinder anode For Alpha I Gen II 1991 and up Magnesium anode for use in fresh water applications Magnesium aftermarket replacement for Mercruiser 806189A2 Replaces Mercruiser 97-806189A2 For aluminum see p/n CM806189A For zinc see p/n CM806189Z