"Mounting Points?", unsure whether the question is directed to jjr2001 or myself.

There is no way to predict size across brands, and so many look alike, branding vs manufacturer is a toss up.
Predominately, a steel body might carry fine threads, an iron casting is certain to be tapped coarse, as would be aluminum. This applies whether the threading is US imperial, British imperial/ whitworth (if its older), and most probable is metric. Few people have samples in each thread form, I'd take it to a fastener house.
Three simple alternatives; 1] converting to closest or next larger size, unless its a commercially made grinding vise; those are through hardened.
2] Design a clamp-on stop.
3] Build a table mounted stop. All things considered, these are the most universal.