Zinc: For use in salt waterAluminum: For use in brackish waterMagnesium: For use in fresh waterRUDDER & TRIM TAB ANODES WITH ALLEN SCREW (MARTYR ANODES)SKU: 6.28309E+11$22.29PriceQuantity*Add to CartFeaturesSize2-13/16" dia. x 1/2"MaterialMagnesiumCase50