This ring is actually two (or more) rings. The main sterling band (which will actually go on your finger) is made and then one or more rings are made to closely fit over top of the inner band. Then, the inner band is bent outwards at both edges to hold captive the outer rings, which then spin freely on the inner band.
I personally love things that you can play with when I'm bored, and I hope you do too.
Let me know when ordering if you have any special requests for metal types for the spinner parts when ordering, otherwise the default will be two silver rings (subject to change to accommodate ring size while still looking good).