I think that I have a thread gauge in the toolbox... recently dedicated a small toolbox just for anything thread related. There should be one in there...
Sometime in the 1990s, Grizzly changed vendors. The earlier model was G-1550, which is what I have. When they changed over, the new part number was G-4000. They are essentially the same machine, the G-1550 having a 1-1/2X8 TPI spindle nose and the G-4000 having the M39X4. There are some minor differences, fasteners being Imperial versus Metric, things of that nature. That and the source, the G-1550 being made in Taiwan and the G-4000 made in Mainland China.
There are many different importers of this basic (standard?) design. Most of them I will avoid, with the exception of Enco and the
JET BD19. Not too sure of the number, it doesn't ring true to my ears. But close, just follow it up until you find a similar number. The Jet is a very well built machine, with a history similar to the Griz G-1550. I don't know if they changed to the cheaper version or not. Jet seems to market to a slightly different field than does Grizzly. And is priced a little higher. All in all, the color of the paint is the biggest difference. Enco is directed more to the metal working market, Jet and Grizzly mainly woodworking.
Now, in
reply to your post above, there are three(3) thread forms you need to be aware of up front. Those being
Imperial (USS, SAE, others).
Metric (and SI), and
Whitworth. There are
many more, but these three are so easily confused. Each will have a different guage, what is in your tool box will probably cover just one. If you use an Imperial guage and a leaf almost but not quite fits, it is likely metric. Whitwirth is a now archaic English thread that will show up on older English equipment. They are today metric. Imperial and metric are a 60 degree thread form, Whitworth is 55 degrees. The rabbit hole gets deeper and deeper. . . Sorry I am being so verbose, I dropped into lecture mode.
As far as a
four(4) jaw chuck goes, I learned on a four jaw 'way back when. The 4 jaw is still my preference for any "precision" work, although I mostly use the 3 jaw. My 4 jaw came from Grizzly without a backing plate. I had to make one to fit. The big advantage there is that when you go to a different machine, the backing plate is the only change. Mine is a 5 inch, a 6 inch would have been better but the 5 inch costed less. For a novice, the 4 jaw will require you learn to mount the work. Well worth the effort, but not critical. The 3 jaw will serve you well until you learn to do serious work. I would say to put a 4 jaw on the options list and keep it near the top. Had I had a 3 jaw early on, I would have used it more. But learning on the 4 jaw has paid off from time to time.
EDIT: A good purchase at this point would be a copy of "Machinery's Handbook". At about 3 inches thick, it contains
most information necessary for the novice. It is updated regularly and contains much information useful to a practising machinist. My recommendation would be to look on eBay for a copy from the '40s or so. Much better for the hobby machinist without all the leading edge automation. It sells high from booksellers, but can be found for much less if you watch and wait. I have a very early copy(1933ish) and a recent copy(2005ish) as well. Both have a place on my bookshelf but gather dust. The one on my bench is a 1944 edition, the one with the most useful information.
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