NEW! Improved Design! Also works on competitors air diffusers and air returns. Don't know your neck size, no need to measure! The Eger Advantage Universal Collar reduces the neck from a 14" to a 6", 8", 10" or 12" neck. Easy installation - The neck size "diameter" on the universal collar can be easily cut onsite using a box cutter or utility knife at the time of installation. Won't collapse, easily slide the flex duct over the neck of the Universal Collar.