SureFlap Cat Flap Tunnel Extenders can be used in wall installations to create a longer approach for the SureFlap Microchip Cat Flap. The tunnel extender fits onto the outside of the pet doors integrated tunnel and you can stack multiple extenders together up to any length. The tunnel integrated into the pet door is 70mm long and each tunnel extender adds 50mm. Can be used with: Sureflap Cat Flap Mounting Adaptor Sureflap Cat Flap Tunnel Extender