Cup burs are basically a file inside a cup. Use cup burs to eliminate sharp wire ends in jewelry making. This is especially important for ear wires and earring posts, but can be important for any ends in wire wrapping, that could potentially poke or scratch. After clipping wire, gently insert cut end into cup and rotate. The end of the wire will become smooth with a slight dome. Click into any cup bur / wire rounder tool below to see additional features, or which sizes of wire each works best for.