Chainmaille Ring Sizer Tool (Outside Diameter)

While working with various ring sizes, I've often picked up a ring and wondered what size it is. This solves the problem without the need for calipers or a ruler. Measurements are in inches and millimetres, so conversion can also be done. This particular ring sizer measures outside diameter. (OD)

You can find the one that measures inside diameter here:
http://www.thingiverse.com/thing:852513