This cup bur is perfect for rounding wire ends. After the ends of wire are cut with a pair of side cutters, the edges are often sharp and can cause snagging. If you are making ear wires in particular, you'll need to smooth the ends of the wire, especially the end that will pass through the ear. This tool will do that. It has teeth like a file inside the cup. Simply place the cup over the end of the wire and twist or rotate the handle back and forth to file and smooth the ends of the wire. This works best for wire up to 20 gauge.