CM31640 Zinc Anode

ITEM	CM31640
MERCRUISER	31640A1, 31640Q 4
FITS	For Use on R/MR//Alpha One (Sterndrive & Transom Assembly 1983-90) & Prior Drives

Do all Anodes Fit Every Water Environment?
The answer is no.  Throughout the world you may find many different water environments which may all require different solutions.  The three main water types are salt, fresh and brackish.  Martyr zinc and aluminum anodes protect very well in salt and brackish waters where magnesium anodes protect the best in fresh water. 
Whenever possible, measure electrolytic corrosion around your boat by using a Corrosion Test Meter.  This will quickly indicate if your anodes are providing adequate protection.