Avoid galvanic corrosion to the metal parts of your rudder.Offered in Zinc for saltwater, Aluminum for salt- or brackish water and Magnesium for freshwater. Stainless steel hardware.Key FeaturesHex-head stainless steel machine screwFor use in salt waterManufactured to meet or exceed US Military specifications (MIL-DTL-18001L) Protects underwater metal parts from corrosive electrolytic actionPressure diecast anodesDome shaped to provide the least amount of drag