Mercruiser Magnesium Gimbal Housing Anode | Canada Metals CM821631M Martyr Magnesium anode designed to protect gimbal housing from corrosion in fresh water lakes and rivers. Mercruiser gimbal block anode current design Magnesium anode for use in fresh water applications Fits R, MR, Alpha One and Alpha One Gen II Fits Bravo I, II, III, X, XR and XZ drives Magnesium aftermarket replacement for Mercury 97-821631T3 Early design see p/n CM43994M For Zinc see p/n CM821631Z For Aluminum see p/n CM821631A