The 5″ sight glass is a bowl that allows you to see the contents of the water tank or cyclone. It fits inside a weldment that has a screw handle. A gasket goes between the glass bowl and the equipment, and a metal plate goes between the tightening screw and the bowl to distribute the force. Do not tighten the screw handle too tightly, or you may break the glass bowl. It only needs to be snug.