Fits current AHN style units with 4 buttons for control below digital temperature display. Models include Eco600, VIGOH77, PRO1100, PRO1300, PRO1400, and PRO1400HC. Installed in water inlet pipe inside heater to measure water temperature entering heater. Sends temperature information to main board for proper heating of water. Has built in spade connector for easy electrical connection to main control board. Some control board connections require the removal of spade connector and stripping of wire. 6 foot total length with wire.