The PetSafe Microchip Cat Door Tunnel Extension allows the PetSafe Microchip Cat Door to be installed into thicker doors or walls, adding 5 cm to the overall depth with each tunnel. Adding the tunnel is simple, with no tools required, and each extension can be secured in to place with glue for a flush, precise fit. Multiple tunnels can be used in order to fit the needed door or wall thickness. Your pet deserves the best. This tunnel extension offers 50mm extra tunnel depth and can be combined with other extensions. It is suitable for installation in walls and doors.