8 X 5 Vent Pipe Reducer - HVAC Ductwork Sheet Metal - Indoor Comfort Supply
Abs Duct Fan Connector Wall Range Hood Flange Adapter Kitchen Air Vent Exhaust Hood 100/120/150/200mm For Ventilation System - Pipe Fittings - AliExpress
PANASONIC Duct Adaptor: Metal - 32NA44|FV-VS43R - Grainger
WhisperValue® DC™ 24 Gauge, fire code rated, 4" oval to 3' round | Crescent Electric Supply Company
GE RAK6053 Duct Adapter for GE PTACs
Air Duct Adapter For 120mm Case Fan 4" and 5" Output – The House of Hydro
Snap-in duct adapter for 4" ducting
Master Flow 4 in. Flexible Duct and Sheet Metal Connector Splice Collar FC4 - The Home Depot
6 Inch to 4 Inch HVAC Duct Reducer & Increaser - Galvanized Sheet Metal Ducting Connector for Airflow, Heating, Cooling, & Air Ventilation System Extra Strength and Fittings - Ducting Components - Amazon.com