I was just goofing around on this. I thought! I thought it'd take about 20 minutes, yet it ended up being about 6 hours! =D That's cuz of having to stick to Shapeways design rules while at the same time making the ring size nominal. This is an US size 10, which is 0.78 inches or 19.81 mm in inside diameter. If you want a size 10 use the buy now button above. Other sizes can be made upon request, just let me know what size you want by using the contact designer button on the right.
I wanted to make this out of lapis lazuli, but Shapeways doesn't have that material! HAHAHA! =D