This tee piece in the horizontal rigid flat duct is part of the Polypipe Domus duct system. This fitting is used to bring together two additional duct runs into one main run, cutting down on the amount of lengths required overall.The whole range has been designed to promote the most efficient energy performance within the ventilation system, eliminating any air leaks or drops in pressure. It is available in two system sizes - 110mm x 54mm and 204mm x 60mm.