The base flange of the sight glass is welded to an open pipe socket similar to DIN 11851 or EN 10357 and thus forms a resilient and tight connection with the rest of the system. On the media side, the borosilicate glass disc, which complies with the DIN 7080 standard, is sealed by a gasket ring made of which is specially shaped for milk pipe screw connections. A groove nut provides the necessary support.