The above answers are correct. As for the glass, the picture is misleading as it is not the correct item. The Cat Mate Elite cat flap can be fitted to single/multi-pane glass up to 10cm thick WITHOUT an adaptor. The round hole must have a diameter of 232mm (check the instructions!)

Hello, I confirm the previous answer. On the box there is the information: Tunnel cut-out cover, use an extra frame every 50mm of thickness. https://www.pet-mate.com

Hello, the maximum thickness is 5cm. For a thicker door, an adapter (not supplied) is needed. The assembly instructions are very basic. A search for the instructions on Google may give you more information.