The Master Flow 4 in. x 3 in. Round Reducer is made of galvanized steel. It features hemmed collar edges for enhanced strength and a secure fit. The reducer is used to transition from a 4 in. pipe to a 3 in. pipe in an HVAC system. It is suitable for most HVAC applications.30-Gauge, galvanized steel construction for durabilityHemmed collar edges for an improved fit and increased strengthConnects 4 in. pipe to 3 in. pipe in duct runSeal seams with code-approved mastic, sealant or duct tape sold separatelyAlways insulate ductwork for greater system efficiency and comfort insulation not included