The thread looks far too fine to be an Acme thread, how about a close-up shot Norm.
More Pics kind sir?
I went digging again and came up with a couple of AWESOME sites on 'Vintage Woodworking Tools" sites.
Papawd, you will be impressed!
This one is about Woodworking History. About 3 paragraphs down is a link to Delta's old 1931 catalog. primary sources -- documents of the woodworking movement
The first line starts with "We get an example..." the word ''catalog'' is the link to the PDF. That leads to this site! VintageMachinery.org | Welcome
So I used their Search box with only the word "Vise" and got a list of all the US patents on Woodworking Vise, from this site: All Patents of Type: woodworkers vises
Just going through them.
Anyway, I haven't figured out how the "Reprints" menu works on that Vintage site. They only show the first most recent uploads from their fans. All of the 4463 reprints are free, copyright free, dowloads of old machinery documents and manuals. So I suggest that you 'RIGHT CLICK" that "CATALOG" link, I mentioned and get it there. It is "FULL COLOR" - Black, White and Red product names.
AND! As an added bonus, for reading my long post, you can get this copyright free book, from here.
"How to make Woodwork Tools" Library - How To Make Things - Toolemera.com
Again! "Right Click and Save As..." it.