Dust Extraction Fitting, Funnel Reducer, 4" x 2-1/4" - Vacuum And Dust Collector Ducts - Amazon.com
Amazon.com: Dust Collection System Adapters Shop Vac Attachments 4 inch to 2.5 inch Reducer 2-1/2-Inch to 1-1/2-Inch Fitting 1.25 to 2.5 inch Coupler Dust Collector Fittings Accessories : Tools & Home Improvement
POWERTEC 4 in. x 2-1/2 in. Cone Reducer for Dust Collection Systems 70136 - The Home Depot
POWERTEC 4 in. x 2-1/2 in. Reducer 70104 - The Home Depot
Large Reducer 100-57mm | Dust Extraction Hoses and Fittings | Extraction | Machines & Power Tools | Tilgear