I don't know why this simple little device gets such bad reviews.  I ordered it to resize a slender band, and it works fine.  You just lay the wire along the bottom, then bend the prongs around the ring. I needed some needle nose pliers to do this, and then needed a little more force to clamp down the ends so they weren't skewering me in the finger.  Works fine, although I could see how this is not an ideal solution to a wider band.