Duff ZSA138 Zinc Shaft Anode - 34.9 mm (1 3/8 in) | 4BoatsThe Duff ZSA138 zinc shaft anode protects propeller shafts from electrochemical corrosion with a durable, golf ball shaped design that is easy to fit and maintain. Zinc construction for sacrificial protection Golf ball shape for even wear and neat appearance Continued corrosion protection for propeller shafts Outer diameter: 67. 6 mm (2. 66 in) Shaft diameter: 34. 9 mm (1 3 8 in) Fits directly onto 34. 9 mm (1 3 8 in) propeller shafts Low maintenance;