Using the mounting adaptor for wall installations enables you to installthe cat door more easily because you can use it to fix the cat door to thewall without the need for messy adhesives. The mounting adaptor is notrequired to install the Microchip Cat Door Connect in a wall as thisproduct contains wall mounting screw holes within the front frame. The CatDoor Mounting Adaptor includes two parts, one for the exterior and one forthe interior of your home and is required to install the SureFlap MicrochipCat Door or the DualScan Microchip Cat Door into glass, walls and certaindoor types. This accessory allows mounting in circular holes with adiameter of 212mm (min) to 260mm (max). The total diameter of the mountingadaptor is 285mm.