love the sterling silver band I bought it for my thumb.  I thought it would fit both thumbs but my right thumb is much larger then my right thumb so I wear it on my left thumb.  never thought of measuring my right thumb thought both thumbs where the same size.  So if your thinking about ordering this ring for you thumb measure both of them.  I wear my ring on my left thumb which I would of got a 3mm but the 2mm is fine just a little thinner.