There is not a very good agreement between standard drill sizes and standard ring sizes, but in this case, close seems to work just fine. This is the reference chart that I use:
Ring size on wikipedia
So for example, to turn a size 8 ring I need a drill that is 0.714 inches. The closest drill is 23/32", which is more like size 8 1/8. An 8 1/8 ring is indistinguishable from a size 8 ring for most practical purposes, but the imprecision bothers me. ;-)
To make a chuck of sorts for these rings, I rip a 2x4 in half and throw a length on the lathe between centres. As I turn a slight cone at the right side for the rings, I end up using more and more of the scrap wood until I have to start over. But the goal is to slightly undersize the chuck so that the ring is a firm fit when a small piece of fine sandpaper is wrapped around the wood. Without sandpaper, the ring just spins and burns.
I've found the bamboo plywood scraps that I use challenging to turn in the past. The bamboo and adhesive tend to dull tools, and using a gouge risks a catch that tears the work in half along a glueline. So I stick with a square scraper to round and then gently roll the outside form of the ring.
All of my small pieces are shipped in a handmade, recycled card box. This one is made from an empty tissue carton.
The rings are worth the trouble. I love the bands of bamboo fibre bundles sliced at different angles.
