This is a normal tile with elliptic central hole of cm 12x16 with a raised rim that permits the passage of ducts until Ø10 cm.
This unit element permits:
to avoid bad smells inside inhabited rooms
to get rid of gas and vapours from the kitchen
to empty the siphons in the bathrooms
resistance to wind penetration
no need for skilled labour
possibility to join more than one flues in the same vent
to keep always a vertical position because it is articulated
weight: kg. 7.