What all does it say around the chuck? Sometimes it tells you arbor size.
Brian, well darn! Then that just means a little longer to figure it out. By taking some measurements of the tapered hole and checking with a chart on Jacobs tapers (should be this?) you can find your answer. There is a bit of a spread between the taper sizes. So you shouldn’t be wondering if it’s this taper size or that taper size. Should be able to find your taper with simple measurements and then compare your numbers to the chart. Good Luck…Dave.First thing I looked at, nada. I emailed Jacobs, no phone contact listed anywhere on the net, guess they don't want pesky customers taking up valuable time. Brian