Thermalwell for Heliodyne probe type temperature sensor. 1/2" NPT pipe thread brass well. Overall length is 2", length of probe is 1 1/2". Can be used in a pipe fitting or in 1/2" side port on Rheem and Sunearth HE solar tanks. Fits Heliodyne well style 10K probe sensor SENS 003 003 (CT-0055). Includes set screw and allen wrench to secure probe into well.