The Petsafe Wall Entry Pet Door is a good utility pet door that utilizes dual flaps. These flaps are the same as those found in the PetSafe Classic pet doors. Flaps are replaceable and we always have them in stock. The tunnel on the PetSafe Wall Entry door is a two piece sleeve that will glide together to fit wall thicknesses within the range of 4 3/4" to 7 1/4". Each door comes with a slide-in thermoplastic security panel. This security panel can be used on either the interior or the exterior side of the pet door.