![[photo] top view of a side sliding window insert](/v/vspfiles/assets/images/ideal_top_425.jpg)
The top spring-loaded adjusting section of the Side Sliding Window pet door appears as an "H" piece when viewed from the side. The overall width of this piece is 13/16" (Will fit into most any sliding window track).
The spring-loaded adjustment provides for a 2 1/2" range for proper fitting into your opening. Most top tracks in sliding windows do not have any center rails, however, if you do have this feature then the top section can straddle any rail at the top 5/8" wide or narrower.
The spring-loaded top is secured with 2 thumbscrew locks, accessible from inside the house only, someone from the exterior of the house would not be able to compress or remove the unit.