Duda Solar alumrod23cm Zinc-Aluminum Anode Rod for Water Heater Tanks & Solar Water Heater Systems Length of anode rod: 23cm/9 Material: zinc-aluminum (10Percent zinc, 90Percent aluminum) 3/4NPT connection Sacrificial anode rod for tanks with hard or Salty water or with sulfur Dioxide smell (rotten eggs) caused by iron Check rod for corrosion annually and replace as needed