6" to 4" Metal Duct Red. CKR64 - Pack of 4

These increasers/reducers allow round ductwork to be increased from 4 to 6 inches or from 6 to 8 inches, or decreased, which is sometimes necessary when you are exhausting from two locations with one in-line fan. They are made of galvanized metal. The actual diameter at each end is 1/8" smaller than the duct it would be secured to.