It is used whebn you use an adapter with the chuck to fit it to other
lathes to prevent the adapter from unscrewing from the chuck body when you
remove the chuck from the lathe.

On Sun, 04 Mar 2007 19:44:02 GMT, "Bob Daun" wrote:

I have used my chuck for quite awhile but I was just wondering why there is
a threaded hole in the back end of the adaptor (the side facing the
headstock when mounted). The threads in the hole are quite fine but there
is nothing in the hole. If I shine a flashlight into the hole I can see the
threads from my headstock. Is this meant to use as and additional hold
down? I would hesitate to do that as it would ruin the headstock threads.
Any thoughts on this?