For wall installations, tunnel extenders can be stacked together to create a longer approach tunnel to the SureFlap Microchip Cat Flap, the DualScan Microchip Cat Flap or the Microchip Cat Flap Connect when it is installed in a wall. The Cat Flap Tunnel Extender fits snugly onto the 70mm long tunnel of our cat flaps. Each tunnel extender adds 50mm to the overall length of the tunnel.