Steve's chisel idea sounds good. the newer cannonballs now have a flattened area around its 'equator' - which enables you to get a better grip for twisting it off. I use a thin layer of rubber (old innertube) and a 'chain' wrench (uses a bicycle chain to wrap and grip around an object). For the new replacement, I tighten it like a spin-on oil filter. the original balls were completely round.