Aluminum Anode Rod - Anode rods preserve the life of a water heater by corroding themselves so the water heater doesn't. Consider using the aluminum rod in areas of harsh water where the magnesium rods last less than 1 year. Just be sure to inspect it every 3 months. If it is mostly eaten away, replace it with a new one to extend the life of the tank. Always keep a spare in your RV toolbox. Aluminum rods are better in areas with harsh water. *NOTE: Use Magnesium rods for Atwood and the Aluminum rods for Suburban and Mor-Flo water heaters.* Rod has 3/4 inch threading. 1 per package.