I have some “hybrid” bearings that I purchased a long time ago on Amazon. They have silicon carbide balls and steel inner and outer races, as you can see in the photos. What I am wondering is what are the other pieces that seem to be holding the balls and covering the balls? Are they likely made of plastic?
I realize that this is hard to answer without any traceability or part number, but clearly these are mass- produced bearings common to many people so maybe someone knows.
The bearings seem to spin very fast without much resistance but also have a lot of play in their non-preloaded condition.
A second aspect to my question is based on this play observed and the fact that there looks like a plastic part in there - could these be some sort of gimmick for use in fidget spinners and not for any actual constrained or load bearing application?
My fault for buying them in the first place but curious if anyone knows more about these mysterious bearings from the cave of alibaba, and the design choices that led them to be what they are.
Edit:
I think this is called a bearing retainer based on the answer below. I found a high end fancy bearing from campagnolo bicycles that seems to have a retainer that looks similar .. so just because it’s plastic doesn’t mean it’s cheap or not good quality. 
