I have Pella screen for sliding patio door.
It goes in the middle of two doors and screen pulls out so that I can leave one side of my patio door open without having to worry about bugs coming in.
Somehow a plastic which holds the screen on top is missing.
image 1 is the bottom and has a white plastic that the screen roll goes in but image 2 is top and is missing the white plastic part to hold the screen showing on image 3.
