A friend just gave me a large lathe chuck and I need help identifing
it. It is 18" in diameter, 4 jaw independant, with an additional 4
slots like a face plate would have. I measured the chuck thread, it has
6 tpi. The diameter of the thread taken by measuring the smallist
diameter on the female chuck thread (I mean I measured from peak to
peak not valley to valley) was about 2 9/16".
Is this a standard thread, if so what is it.

I have a copy of Machinery's Handbook but there is so much info that I
can't seem to find what I am looking for.

This chuck will not fit my lathe, a 7" x 18" atlas. Is it time for
ebay?

Thanks
Paul G