This kit includes new springs and bushings for both sides of the Plexidor (except small cat doors which only have one spring).
If your Plexidor Door model or Plexidor Wall Pet Door is wide open on one side, you have broken a spring. Replacing springs requires removing the pet door from the door or wall, but they come with good instructions and it is not a difficult job. If you are going to the trouble, now is the time to look at replacing the old weather strips on the flaps, or perhaps even replacing the flaps themselves. New flaps have new weather strips already installed.