This is a file I made based on the specs for gymnastics rings from the Fédération Internationale de Gymnastique (FIG) in its Apparatus Norms document. "Inner diameter: 18 centimetres (7.1 in) ± 0.1 centimetres (0.039 in) Diameter of profile: 2.8 centimetres (1.1 in) ± 0.1 centimetres (0.039 in)" I made it in Autodesk Inventor and exported it as an STL file. When I opened it in MakerBot Print it was very small. I had to resize it to get closer to the actual size. Gymnastics Ring 2 has a smaller inner diameter but a larger profile diameter so it might work better if you try to print it on a MakerBot Replicator+ like I did.

Resources: Rings (gymnastics). (2018, March 16). Retrieved March 23, 2018, from https://en.wikipedia.org/wiki/Rings_(gymnastics