PetSafe Wall Tunnel Extension for PetSafe 4-Way Locking and Magnetic Key Cat Doors, White Fits the PetSafe Magnetic Key Cat Door and PetSafe 4-Way Locking Cat Door for installation in interior or exterior doors and walls thicker than 2 1/8" Each tunnel measures 1 7/8" thick and is stackable so multiple tunnels can be added together for any wall thickness White tunnel made from durable, high-impact plastic 1 tunnel included Call, chat or email with our expert US-based customer care specialists six days a week; they are waiting to assist you and your pet with your product needs PetSafe Brand is an industry leading US manufacturer of pet behavior, containment, and lifestyle products since 1991, helping millions of people and pets each year