NDS PVC S&D Increaser/Reducer Coupling, 4 in. Hub X 6 in. Hub 6P07 - The Home Depot
Vent Systems 6" to 5" Inch Duct Reducer Adapter Connector Fitting Pipe Increaser Reducer Cone for HVAC Ventilation Systems, ABS Plastic PVC Pipe 150 to 125 mm - Amazon.com
Vent Systems 6" inch to 5" inch Duct Reducer Adapter Connector Fitting Pipe Increaser Reducer Cone for HVAC Ventilation Systems, ABS Plastic PVC pipe 150 to 125 mm - Amazon.com