Is your door or wall too thick for your cat flap? This PetSafe tunnel extension 310 with an extra depth of 48 mm (1 7/8\") is a great way to extend your cat flap for particularly thick doors or walls. Add a single or multiple tunnel extensions for your cat\'s ease! This PetSafe tunnel extension was formerly known as the original Staywell tunnel extension. It is compatible with the Staywell Deluxe manual 4-way locking cat flap (300 series), the Staywell Deluxe magnetic cat flap (400 series) and the Staywell Deluxe infra-red cat flap (500 series). Delivery includes 1 piece of tunnel extension.