The Conbraco Industries 20-250-03 The 1/2-inch sight glass fitting is a small but essential part of many HVAC systems, such as pumps, boilers, and chillers. Its smooth incorporation into pipelines is distinguished by a transparent glass pane that provides a clear visual representation of the fluid's state. https://www.partshnc.com/20-250-03-conbraco-industries-12-sight-glass-fittings