Hi Bob

The treaded hole is for keeping the chuck spinning off of the
headstock when you have a lathe that can turn reverse or one that can
be stopped quickly.
These lathes have a groove turned for the setscrew to tightened to,
metal lathes all have those grooves.
As your lathe does not have a flat groove, you probably don't need the
setscrew, but if you want to use one than the easiest way would be to
use a nylon/plastick setscrew, it will not damage the spindle thread,
or you could use a plastic plug between the setscrew and the spindle.

Have fun and take care
Leo Van Der Loo



On Mar 4, 2:44 pm, "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?

--
Bob Daun