DN Union Sight Glasses are industrial fittings designed for visual inspection of fluid flow within piping systems. They typically consist of a transparent window, often made of borosilicate glass, encased in a durable metal housing. The DN in "DN Union Sight Glass" refers to the nominal diameter of the pipe connection, indicating the size of the fitting. DN Union Sight Glasses provide a convenient and reliable means of visual inspection, enabling operators to monitor the flow process and identify potential problems quickly, improving efficiency and reducing downtime.