DESC: PetSafe Classic Pet Door's heavy-duty aluminum frame withstands stress from even the most powerful breeds. The soft, transparent, single flap provides maximum energy efficiency. Insulated, locking, rustproof closing cover has a locking pin and is the strongest and most secure available. The adjustable frame installs easily in any door thickness from 1/16" to 2" and may also be installed in walls (additional framing required). Flap opening: 8" x 11"; great for medium pets up to 40 lbs. Shipping weight: 5 lbs.