Magnesium 1/2 inches NPT for atwood water heaters. RV water heater anode rod 4.5 inch long with 1/2 inch pipe thread. Extend the life of your RV’s water heater with Camco’s patented magnesium anode rod for aluminum water heaters (Atwood style). Camco’s RV water heater anode rod preserves the life of your water heater by corroding itself so your water heater tank doesn’t. Simply replace your 1/2 inch pipe thread drain plug with the Camco RV water heater anode rod to protect your tank.