Provides comfortable access across wider doors Extension tunnel for use with PetSafe Classic Cat Flap when the door or wall is too deep for the cat flap. Single or multiple extensions can be used as necessary to form a comfortable sleeve between inside and outside flaps. The Classic Cat Flap can fit doors windows and walls of up to 57mm depth and wider if optional tunnels are used. Each Classic tunnel can add 17mm depth to the overall sleeve. So using one tunnel will accommodate a door width of 74mm 2 tunnels will accommodate up to 91mm etc. Features & Benefits Fits the PetSafes Staywell Classic pet door Multiple tunnels clip together for increased depth Each tunnel extends sleeve by 17mm Strong and durable plastic Provides more comfortable entry Fitting and Usage Fitting instructions and cutting template are included with each pet door.