The ring has an ID (thats the actual finger measurement) of 22mm. i've included the  curve file as well, so you can import it into your modeling program, and revolve it to create a ring of the desired size. 

Once the ring is printed, complete any post-processing you desire, such as sanding, and removal of the support flare at the bottom. carefully use a blade to trace the join between inner and outer ring, as it will likely need some convincing at first before it spins.

clearance between the inner/outer ring varies between ~0.25-0.35mm.