All metals immersed in an electrolyte (sea water for example) produce an electrical voltage. When two dissimilar metals are in contact (electrically connected) they produce a galvanic cell (like a battery), with the less noble metal (Zinc) for example forming the anode and the more noble metal (Stainless Steel) forming the cathode. The anode sacrifices itself by corroding (giving up metal) to protect the cathode - hence the term sacrificial anode.Why Are Performance Metals Premium Anodes Better?Performance Metals anodes are made from Aluminum/Indium alloy. This Aluminum/Indium alloy is more active so it gives better protection than Zincs. Aluminum anodes are essential for Mercury sterndrives. Zinc will not provide the correct protection for this application. Mercury recommends aluminum anodes for both salt and freshwater on their sterndrives. Aluminum anodes last 40% longer than zinc anodes. Aluminum anodes "self-clean" in fresh water. Zinc anodes form a coating that stops them working within a few months. Performance Metals premium aluminum anodes come with the required hardware for mounting.