Patent Pending adapter matches the contour of the OEM roof so a standard RV style vent mounts to a flat surface. Prevents distorting the roof sheet metal or vent flange and can be used as an aid for locating the fan. They are CNC machined out of UV and fire resistant expanded PVC. The fan mounts to the outside adapter. Fan adapters work with the Maxxfan Deluxe series and the Fan-tastic Vent fans.