Warming: The size S is for flat door or window, which do not need screw, just glue it together. 

----***FYI: Package is not included glue.***

Pet Door Interior Door Sliding Door for Cat, Small Dog, Rabbite, Exterior Safety Door with 4 Modes (4 Ways) Locking, Weatherproof Pet Door, Suitable for Thin Window, Door and Wall - Size Small / Medium / Large / Extra Large

Features:
    Freedom & Convenience - Through the great cat door, your cats or small dogs can go in and out easily and quietly. They won’t feel trapped and you no longer bother to open or close the door for them.
    Safer with 4 Lock Modes - By slide the switches, you can adjust the access mode to Free In & Out, Fully Locked, Out Only, In Only, control your pet’s access and keep away stray animals.
    No Tunnel Part, No Need to Cut - The panels are only (Size S - 0.78in) / (Szie M/L/XL - 2.16in) thick and tightly fitted, suitable for windows, wooden door and sliding glass door, etc.
    High Quality --- Made of ABS material, weather-resistant, the surface is smooth. It provides a fixed groove with snap tabs for weather-proof brush strip, firmly fix the brush strip. Even if the brush strip comes off, easy to put it back into the fixed groove. This greatly help the brush strip reduce noise, stop rain drop, wind or pest like mosquito to the most.
    Simple Installation - Package includes detailed instructions (with templates on), screws set and caps, double-sided tapes. You can cut the template off and install the cat door for sliding glass door easily.

     --- Simple Installation:
1:Stick the REAR panel on the door with double-sided tape, and use a pen to draw around the OUTSIDE of the tunnel part of the rear panel.
2:Remove the rear panel and use an electric saw to cut out a tunnel hole on the door or wall.
3:Put the cat door into the tunnel hole.
4:Tighten the screws with a screwdriver, then add the screw caps.

Size S   --------Please notice the difference thickness between Size S and other.
Outer Frame Size: 19 x 1.8 x 19.7 (cm) / 7.48 x 0.7 x 7.76 (inch)
Inner  Frame Size: 16 x 15.7 (cm) / 6.3 x 6.18 (inch)
Suitable for PET: Weigh ≤ 4kg; Height/Width ≤ 15.7cm

Size M
Outer Frame Size: 19 x 5.5 x 19.7 (cm) / 7.48 x 2.16 x 7.76 (inch)
Inner  Frame Size: 16 x 15.7 (cm) / 6.3 x 6.18 (inch)
Suitable for PET: Weigh ≤ 5kg; Height/Width ≤ 15.7cm

Size L
Outer Frame Size: 23.5 x 5.5 x 25 (cm) / 9.25 x 2.16 x 9.84 (inch)
Inner  Frame Size: 19 x 18 (cm) / 7.48 x 7.08 (inch)
Suitable for PET: Weigh ≤ 6kg; Height/Width ≤ 18cm

Size XL
Outer Frame Size: 25 x 5.5 x 27.7 (cm) / 9.84 x 2.16 x 10.9 (inch)
Inner  Frame Size: 22 x 20 (cm) / 8.66 x 7.87 (inch)
Suitable for PET: Weigh ≤ 12.5kg; Height/Width ≤ 20cm

Note:
1.There will be some error (≤3cm) in manual measurement, please prevail in kind!
2.Before placing an order, please choose the right size!
3.Please notice the difference thickness between Size S and other.

Package:
1x Pet Door