The Honeywell 121371A 1/2-Inch Copper Well with 3-Inch insertion is designed to house temperature sensors in hydronic heating and cooling systems. Installed in boilers, chillers, and other HVAC equipment, it allows sensors to measure water temperature accurately without direct fluid contact, protecting the sensor from corrosion or damage. https://www.partshnc.com/12copperwell-3insertion-2