MRCOOL M14HSR4260A Signature Series 3.5–5 Ton Round Adapter Kit is an HVAC installation accessory designed to connect compatible air handlers or furnaces to round duct systems. It works by providing a secure transition between the unit’s rectangular outlet and round ductwork, ensuring proper airflow distribution and minimizing leakage. https://www.partshnc.com/mrcoolr-signature-series-square-to-round-adapter-kit-m14hsr4260a