0.875" D Zinc Barrel Collar Shaft Anode with Slotted Screw (CMX02S) by Martyr. Looking to protect your boat from corrosion that can occur in salt, brackish or fresh water? Then premium-grade Martyr anodes are the way to go. Pressure die-cast and made of a specialized alloy based on the US Mil Spec they offer corrosion protection and longevity unmatched by the competition. Plus, these anodes are rigorously tested in the companys state-of-the-art laboratory, so you can rest assured of their superior quality.