Size Name:4" Inch // 100mm PLASTIC RECTANGULAR AND ROUND SYSTEM Plastic air ducts are designed for use in small living spaces and office premises, where the ventilation system is most often locted under a suspended ceiling. Plastic rectangular or round system allows easy installation of small air lines with different turning angles for the horizontal and vertical planes, due to the available convenient auxiliary connections and adapters. Check REPA MARKET for more compatible and similar products with high quality.