Hi, folks - just stumbled on this illuminating post yesterday; fantastic info! I see that you're dealing mostly with the "big boy" vises and, at risk of courting ridicule, want to share some pics of an old vice I inherited from an even older uncle who worked, mid-1930s 'til 1970s as a machinist in a sugarcane mill. This is a simple, portable vice that I actually use a lot when I need to clamp something wherever I'm working, and am away from the bench vices.
The sole inscription is the three letters and the number: they don't come through very well in the photo but I think they are "R H S" and "30" - they seem so primitively stamped that maybe they're just someone's initials hand-stamped in for ID purposes (they're not my uncle's initials). It's so primitive I'm wondering if perhaps this is something that they cast themselves at the mill?
Any comments appreciated. And many, many thanks to everyone who has contributed to this forum. Aloha.