Direct from the rules and regs:
The dumbbell, which must be approved by the judge, will be made of one or more solid pieces of wood or non-wooden material similar in size, shape and weight to a wooden dumbbell. Metal dumbbells are not permitted. Dumbbells will not be hollowed out. They may be unfinished, coated with a clear finish or may be any color. They may not have decorations or attachments but may bear an inconspicuous mark for identification. The size of the dumbbell will be proportionate to the size of the dog. The