Thermal well for Johnson A419 and Ranco ETC controls. Used for submersing the temperature probe in liquids. Copper bulb 1/2" NPT, 2 3/8" long. Includes compression spring to ensure sensor contact with the bulb.
Note: This is not recommended for use in aquariums because the copper may be toxic to fish, corals or other aquatic life. In this application stainless tubing or the cheaper PVC or vinyl tubing is recommended.