The SureFlap tunnel extension is an accessory that can be used to extend the tunnel of the microchip-controlled SureFlap pet door when installed in a wall. The extension pieces fit perfectly onto the tunnel of the microchip-controlled SureFlap pet door. You can connect multiple of these elements in a row to create a tunnel of any length. The tunnel of the SureFlap pet door is 70 mm long and is extended by 50 mm with each extension piece. Using the illustrations on the right side, you can determine how many tunnel elements you need for your wall.