I thought of both those possible responses, but it looks too big to be a typeface locking clamp, and too roughly made to be a machinist's screw jack - I reckon the answer's still out there somewhere...
I guess if this one is an 8" lock(ing clamp), there may be other sizes out there as well..... bigger and/or smaller???
The tapered nut arrangement looks like some sort of quick release adjustment, to allow rapid insertion without having to fully wind out the screw - I think we need to look at something that needs to be 'locked' in place, e.g. holding some workpiece on a machine, or maybe locking up a machine (steam engine??) while it is being worked on....
Apart from these few 'gems of wisdom' (????) I've no idea.....