Well it looks like a 1/8" hole might work for my application, I am running this on a taig lathe probably not going to exceed 3500 RPM, so from the website the slot width or angle is (alpha=.0012xN) or 4.2, so with my 2.5" diameter disk should be (W=.0088x alpha x dia) or .0924, I still may drill 2 holes next to each other and file out between them to increase my capability to say 5000 rpm when I am not using a chuck. Please check my calculations math is NOT my strong point! I just didn't want to make a finger remover by making open slots which is why I am looking at keeping this compact and using drilled and filed holes.