From the Flip A Card schematic:
Flip A Card ring chart (resized).jpg
/Mark

Ha, I never checked the chart that Mark posted but I recently replaced rubbers on mine with new ones from PBR and I saved the bag full of the old ones I got off EBay a couple of years ago.

In the old bag were:

3- 3” rings
3- 2” rings
2- 1 1/2” rings
1- 1 1/4” ring
3- 1” rings
1- 3/4” ring
20- 5/16” rings
And 1 rubber backstop ring

Maybe over time companies selling them changed the sizes here and there or maybe they sent some incorrect sizes but I don’t remember any issues with too loose or too tight fits.

Interesting but either way Im guessing the OP should stick with the chart.