I'd be holding on to that one!!!!!! The Thomas Vise is what Harry Darbee, one of the well known Catskill fly tyers used. Looking at the condition of your's I'd say check out this thread http://www.sparsegreymatter.com/viewtopic.php?f=17&t=1013 Don't know if you'rs has the sticker on it or not but since you have the box just as good I think.
The base ain't right on this one - I do have one that is a precursor to the Xuron. It has the hole in the stem and I have the thread clip that goes in it. I'll post some pics of it tomorrow.
Lots of guys were wondering what that hole was for and someone said clip. That Thomas vise is a part of tying history with the Catskill guys. For some that have tried it they say it's really good.