I have a few Sjogren-Hardinge speed chucks and I always thought the small handwheel, 7 3/4", were the high speed chucks as used on the 10EE. But one is a A2-5 mount with a 10" handwheel and it's marked don't exceed 4000 rpm. I do have the small handwheel version also marked don't exceed 4000. These are both 2J collets. What's the difference between an unmarked chuck and 4K chuck?