Required for glass and wall installations, this product can be used with the SureFlap Pet Door Adaptor. When mounting in glass, this accessory allows mounting in circular holes with a diameter of 294mm (min) to 320mm (max).***Please note: Only suitable for SureFlap Pet Door and not the SureFlap Cat Flap. An appropriate adaptor for the Cat Flap is available***The total diameter of the mounting adaptor is 285mm. Using the mounting adaptor for wall installations enables you to install the cat flap more easily because you can use it to fix the cat flap to the wall without the need for messy adhesives. The Cat Flap Mounting Adaptor includes two parts, one for the exterior and one for the interior of your home.