Cobra Zinc Cavitation Plate Anode | Canada Metals CM984513Z Zinc Martyr anode protects OMC Cobra gearcase from corrosion in salt water. OMC Cobra cavitation plate anode Zinc anode for salt water applications 5.7 in long 4.1 in. wide 1.6 in. high Bolt hole spacing 4.44 in. on center Direct replacement for OMC 984513, 3853818