Sureflap Tunnel Extenders from Sure Petcare fit snugly onto the tunnels of Sure Flap microchip cat flaps & 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 Sure Flap Microchip Cat Flap & the Sure Flap Dual Scan cat flap, whilst the Pet Door tunnel extenders are compatible with the Sure Flap 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 & details of your Sure Flap product before ordering to ensure you have the correct Sureflap Tunnel Extender products Sure Flap Cat Flap & 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 Sure Flap microchip Cat Flaps & Pet Doors are 7cm long & 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 & Pet Door not included.