I haven't taken them out yet ........Just curious. Do the lower set screws have brass, or bronze tips?
One of my machine vises has a double set screw like that to hold the moving jaw to the nut. It's an older import that came from Taiwan as well. I bought it at an auction and it was still in the original packing that had to be 20 years old.OK, I took a more careful look and found that under each set screw, there is another set screw of the same socket size.
It appears that the top screw is for locking the one beneath it. Now I tend to believe that those screws serve the purpose mentioned by dbb-the-bruce in his reply above, ie, adjusting the fitting between the movable block and the vice bed like those for adjusting the gibs of dove-tails. Has anyone seen such design on vices ?