This PetSafe Big Cat Flap Glass Installation Adaptor allows you to install the new and improved PetSafe Big Cat Flap into a glass door or window. The kit includes two installation adaptor frames, a glass cutting template, and installation hardware. A gasket on the back creates a weather seal between the glass and the adaptor. Please note that the cutout in the glass must be done by a professional glazier and should be done at the time of door manufacture for multi-pane and tempered glass. Your pet deserves the best. Trust PetSafe to keep them healthy, safe and happy.