Sight glasses allow visual inspection of the flow of a medium through a transparent window in a coupling. They can be installed at various points of a loading/unloading system. The sight glasses are made of aluminium or brass. They come in 2″, 3″ and 4″ sizes with various connections: male thread, female thread, flange, CAMLOCK. The sight glasses are used in fuel, petrochemical and chemical loading/unloading applications.