Mercruiser Zinc Button Anode | Martyr CM55989Z Martyr zinc button anode designed to protect gimbal housing from corrosion salt water. Mercruiser button anode Zinc anode for salt water applications For gimbal housing mounting bolts on Mercruiser Alpha 1 Gen 1 For gimbal housing mounting bolts on Mercruiser Bravo I, II and III drives from 1988-1995