Reduces installation time by up to 80%. The Simply Stepped collar is designed to accommodates 6,7 or 8" round ducts. Unneeded section is removed using tear away bands. The entire assembly, which includes a damper, fits into a 9" diameter hole. The 4 unique mounting clips with pre-mounted screws secure the unit without the necessity of drilling additional holes. The MV Diffusers are manufactured using advanced high-grade plastics, which will not yellow, discolor and they are resistant to scratching.