The PetSafe SmartDoor Wall Conversion Kit lets you install the Electronic SmartDoor in thick walls and doors. These products are intended for use in traditional framing and drywall construction (2x4 or 2x6). For brick installation, the outdoor cutout needs to accommodate the wall entry frame to be recessed into the brick. With this kit, your small SmartDoor can fit in walls up to 8 inches thick. The large SmartDoor can fit in walls up to 7 1/4 inches, plus an additional 2 3/4 inches with each additional extension tunnel (not included in this kit). PetSafe brand is here to help you and your pet live happy together.Features:• Easy Installation - Kit allows for easy installation of the Large PetSafe Electronic SmartDoor in any interior or exterior wall up to 7 1/4" thick• Telescoping Design - Telescoping design allows for quick installation by framing wall cut-out• What's Inside - Kit includes exterior frame, tunnel, installation hardware, cutting template and detailed installation instructions• Specifications - For installation in interior or exterior walls 4 3/4" to 7 1/4" thick; thicker walls require the Wall Tunnel Extension for the Large Electronic SmartDoor, sold separately. Cut out size: 14 7/16 x 21 15/16 inches