What's the "Small hole in ring" on the lower CR used for? It shown on this page, then never heard or seen from again? Wondering if there's any aligning issues w the fuel tubes?
You will find that the CR with the small hole is slightly larger than the other two centering rings on that sheet.
So I'm guessing the small hole is an identifier so you don't mix up the CRs.
The hole serves no other purpose that I can see.