Help identify large lathe chuck

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
Paul G
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Based on the information given it would appear to be a 2 3/4" - 6 thread. A standard thread as identified in M.H. 25th edition page 1644, Table 3e 6 Thread Series. Look down the Minor Diameter (Internal Thread) column and find the minor diameter that closely matches your information.
When you ask "Is it time for Ebay" are you proposing selling the chuck or buying a lathe that it will fit? Inquiring minds want to know!
Errol Groff
Instructor, Machine Tool Department
H.H. Ellis Technical High School 643 Upper Maple Street Dantieson, CT 06239
New England Model Engineering Society
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Errol Groff

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