Holds pearls, beads, and other round objects. The hardened bushing guide at the top of the jig has a hole in it to keep your drill bit aligned, making it easy to drill a hole exactly through the center of the sphere. Holds spheres from 3 to 22 mm in diameter. Kit Includes a double ended pearl drilling bit: In order to drill straight and precise holes through pearls, it is best to use this type of pearl drill. These double-ended, special profile tungsten vanadiu Bead not included.