This part is on the top of the glass door on both ends and acts as a guide for the door in the top track. I have one missing that allows the metal of the door to grind against the track. The door will not slide easy.
Paul from SWISCO responded:
August 11, 2019
I noticed you recently ordered the 80-045 sliding patio door guide. I also believe this is a match for you as well. Please be sure to get back to us and let us know how everything works out for you.