The Top Hat Adaptor 1mm 316 stainless steel is installed at the base of the chimney on the under side of the register plate. It has a rebated connection on the underside of the plate to allow the connecting flue to slide up 100mm allowing easy integration of the stove / disconnection of the stove. The adaptor to MI-FLEX sits above the plate where the transition to flex should be made. The adaptor has a square cover plate built in to cover the hole made in the register plate.