PetSafe 4-Way Locking Cat Flap 4-Way, knob-style lock gives you 4 options for complete control of your cat's access in and out of your home: open, locked, in-only (cat can enter but not exit) and out-only (cat can exit but not enter) High-impact, white plastic frame with a transparent, hard flap that cats prefer for comfort and ease of use U-flap system helps keep weather and drafts out of your home Easy do-it-yourself installation with detailed instructions, cutting template and hardware included For installation in interior or exterior people doors 1/16" to 2 1/8" thick; Installation in thicker doors or walls require the PetSafe Wall Tunnel Extension which adds 1 7/8" (tunnels are stackable for any thickness) For small cats or dogs 15 lbs. or less; flap opening size 6" W x 5 1/8" H Call, chat or email with our expert US-based customer care specialists six days a week; they are waiting to assist you and your pet with your product needs PetSafe Brand is an industry leading US manufacturer of pet behavior, containment, and lifestyle products since 1991, helping millions of people and pets each year