Sureflap tunnel extenders 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