Hi Ken
I don't have a good used one on hand but you can get one for about 40.oo bucks that's not to bad, right ?.
It's real hard to find a good used one I have tried most of the ones you find are shot, not good for parts most of the time.
Most have the threads screwed up,cross threaded one time or another.
And as you know the 3/4-16 thread must be true,you don't want it to come off and roll around the shop floor with your name on it.
Bottom line, buy a new one at 40.oo bucks, I'm sure you will glad you did.

if you can get the one for the 100.oo bucks go for that one.
The one for 100.oo bucks comes with a tee type tool that makes it easy to lock the stock in the chuck,the other one will use the 2 rod type tool,it's not and easy but it works great.
Just a user tip,,Note***if you pickup a LONG rod tool and let it rest on the bed and then use the short one to spin the chuck and lock it in,this makes it a bit easier to hold the stock in place and lock it down..
But don't forget it's in the chuck b/4 you turn it on.
Wood Chuck 3/4" x 16 TPI
one at 42.oo bucks and one at 100.oo bucks.
http://www.grizzly.com/products/g8783
http://www.grizzly.com/products/h6264
Bj
