Some windows are simply too wide for a standard pet door insert, which is why this version stretches across a 5-inch adjustable range to cover 35 to 40 inches. It uses the same aluminum frame and glass panel construction as the rest of the lineup, with a 7.6 x 10.3 inch flap your cat can pass through easily. The 4-way lock ring switches between in-only, out-only, two-way access, and a full lock, useful for keeping your cat indoors at night or shutting the door entirely when guests visit. A magnetic closure and brush-lined edge keep the flap sealed and quiet as your cat moves through, helping the room hold its temperature. Setup is tool-free, sliding into the window track and tightening the side knobs without drilling. Because the frame itself runs 1.6 inches thick, measure the inner track if your window opening is wider than that, or the outer track if narrower, and confirm your window falls within the 35 to 40 inch range before buying. At 8.8 pounds, it's the largest and heaviest option in this size range.