The center axle of my top was going to be 4 mm. I am trying to keep everything metric. But a 4 mm drill bit in the center hole of my aluminum master part wobbles. Well, my drawing states that all tolerances are +/- .1 mm, and maybe it is within tolerance, but that wobble doesn't make me comfy. Also, upon examination, 4 mm seem a bit slim. So: I am expanding it to 3/16", but I can't drill it on my lathe - too big. Sweating bullets attempting to exactly center the drill on my drill press.