Cast iron double tongue-and-groove cover and grating with square frame and circular opening. The frame seating and the cover bearing edge are provided with a double tongue-and-groove profile, greased to ensure hydraulic watertightness. Perfect fit on PVC and PP inspection chambers (not on the collar). Provided with a bituminous coating to prevent corrosion. A prefabricated concrete seating ring can also be used to provide the necessary support for the cover. Suitable for pedestrian traffic only. Frame supplied as standard with DRWA marking.