These retainer clips are 3D printed exact replicas of the originals that crumble and fall apart. These small brackets hold all the little vent fins together to they move in unison. When these clips break then you will be unable to direct airflow up, down, left or right properly.
There are two clips per vent, one large and one small. This is for one set to repair one vent. The center vent would need two sets.