4" x 2" NPT 304 Stainless Steel Reducer Coupling, Class 150
Amazon.com: 4 inch to 2-1/2 inch Reducer with 4 inch Flexible Cuff Rubber Coupler Fitting and Stainless Steel Hose Clamps with Turn Key Thumb Screw to Easily Tighten and Loosen • Designed
G1/2'' (M) x G1/4'' (F) Stainless Steel Reducer for Pressure Gauge | Tameson.com
Amazon.com: Universal 2.25" ID to 3" OD Exhaust Pipe Adapter Connector Reducer 304 Stainless Steel 2.25 Inch to 3.0 Inch 2 1/4” ID to 3.0” OD kit : Everything Else