The SureFlap Microchip Tunnel Extensions can have unlimited number of tunnel extensions added to accommodate any wall depth. Each extension measures 2" in thickness. The Sureflap Microchip Cat Flap can fit up to 2 3/4" applications, so measure your complete wall depth and subtract this 2 3/4" measurement to determine how many extensions you will need to order (if you have a 6" thick wall, you will need 2 additional tunnel extensions). The SureFlap tunnel extensions are only available in white.

SureFlap Microchip 2" thick Tunnel Extensions for use when installing the SureFlap Microchip Cat Flap into a wall.

SureFlap 2" tunnel extensions