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.

• Manufacturer Model # (6 to 4): CKR 64
• Manufacturer Model # (8 to 6): CKR 86