1 3/8 inch Magnesium Streamlined Shaft Anode | Martyr CMX06M Magnesium Martyr anode protects inboard boat's prop shaft from corrosion in fresh water lakes and rivers. Streamlined inboard propeller shaft anode Designed to mount to 1 3/8 in. diameter prop shaft to protect from the corrosive effects of stray current Magnesium anode is for use in fresh water applications Martyr anodes are made of a high purity specialized alloy based on the US Mil Spec Anode secures to prop shaft with 2 interlocking halves and allen head bolts with bolt retaining washers 1 3/8 in. inside diameter 2 1/2 in. outside diameter 2 1/2 in. length