The SureFlap Pet Door Mounting Adaptor is required to install the SureFlap Microchip Pet Door or SureFlap Connect Pet Door into a glass door. When mounting in glass, this accessory allows mounting in circular holes with a diameter of 294mm (min) to 320mm (max). The total diameter of the mounting adaptor is 380mm. The Pet Door Mounting Adaptor includes two parts, one for the exterior and one for the interior of your home. Please note, this adaptor is not required for wall installations, as the pet door has internal screw holes to enable fixing to a wall.