Works pretty well!
Small springy rolls of silicone-like clear rubber.  They sent 3 different sizes, for different ring shank widths.  Just twist it on the back several turns, and cut it off.  Not only does it reduce the ring size by about 1 size, it also creates a sort of resistance, that keeps my heavy gemstones from spinning to the back of my finger.  Arrgh, I hate that!  lol  It's not harder to put the ring on, either, because it rolls as you slide the ring down your finger.  (And for 3 bucks, the price is right, too.  :-)
Rating: 5 stars