Check the listing for details. 4" to 3" Round Duct Reducer Increaser Connector BATHROOM KITCHEN Steel Adapter. Color: Silver, Condition: New. Listed at 31.41 USD. Description:Material: Galvanized Steel Color: Silver Tone Biggest Outer Dia.: 100 mm / 4 Inches. Smallest Outer Dia: 80 mm / 3 Inches. Length: 210 mm / 8.3 inches. Package List: 1 pcs Duct ReducerAdvantage: The duct adapter is made of galvanized steel material, which is not easy to rust and corrode, and the surface is treated very smooth.Galvanized iron retains the strength and toughness of ordinary carbon steel, so it has certain mechanical properties. Galvanized iron has better fire resistance than ordinary steel. And the ventilation resistance of galvanized air duct is small and will not cause noise.Instruction: Raised lip on both openings allows connecting ducts to get a better grip. Once installed, reducer should be secured with clamps or any preferred fastener.