When I create a ring solid such as the example, often I find that the surface and edges are not continuous. I usually create it by extruding two coplanar closed circles or a flat surface or use a solid offset. What causes the model surfaces and edges to not be continuous as with the attached example?
MergeCoplanarFaces will merge the flat surfaces on the ends of the ring, but will not merge the curves surfaces.
The curved surfaces can be merged using MergeSrf
Explode the ring
MergeSrf Smooth=No Roundness=0
Select the two inner or outer surfaces to merge
Enter to complete