Sureflap Tunnel Extenders from Sure Petcare fit snugly onto the tunnels of SureFlap microchip cat flaps and pet doors. You can use these accessories to create a longer tunnel entrance, for example if you need to install your Sureflap cat flap in a thicker outside wall. Multiple extenders can be stacked together to form a tunnel of any length, making even the trickiest installation a lot more simple to achieve. The Cat Flap tunnel extenders are compatible with the SureFlap Microchip Cat Flap and the SureFlap Dual Scan cat flap, whilst the Pet Door tunnel extenders are compatible with the SureFlap pet door. You can find detailed installation instructions for the Sureflap Tunnel Extender in the relevant product user manual. Important: Please check the the manual for instructions and details of your SureFlap product before ordering to ensure you have the correct Sureflap Tunnel Extender products SureFlap Cat Flap and Pet Door tunnel extenders at a glance: Cat Flap Tunnel dimensions: 14.2 x 12 cm (W x H) Pet Door Tunnel dimensions: 18 x 17cm (W x H) The standard tunnels of SureFlap microchip Cat Flaps and Pet Doors are 7cm long and each tunnel extender adds 5cm to the length of the cat flap's tunnel. Several tunnels can be attached to each other. Please note: Cat Flap and Pet Door not included