The wall conversion kit lets you install the SmartDoor™ Electronic Pet Door in thick walls and doors. These products are intended for use in traditional framing and plasterboard construction (50 mm x 102 mm or 50 mm x 152 mm). 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™ Electronic Pet Door can fit in walls up to 200 mm thick. The large SmartDoor™ Electronic Pet Door can fit in walls up to 184 mm, plus an additional 70 mm with each additional extension tunnel (not included in this kit).