The Master Flow 4 in. Starting Collar has a snap-together design for easy assembly. This starting collar can be used to transition from a flat surface such as a lined or duct board plenum to round pipe or insulated flexible ducts. Can also be attached to metal surfaces. Made of galvanized steel, this starting collar is made for durability. The 2 in. space between the bead and flange provides you with plenty of space for securing an insulated flexible duct. Features: Made of galvanized steel Helps transition from lined or duct board plenums to round pipes or insulated, flexible ducts Can be used with unlined, metal plenums Snap-together design 2 in. between bead and flange allow space for securing insulated flexible duct Seal seams with code-approved mastic, sealant or duct tape (sold separately)