I have used this vise in the field and it's a slick little outfit. 3 1/2 in jaws, no markings that I see. A 1/2 hole in a trailer floor and you have an instant work bench

I use one like that on my drillpress table as it will go through the central hole and then I can crank the table to whatever height is best for the job I want to do in the vise.

I have a very similar one I picked up at a flea market, I welded a square rod on the bottom so I can plop it into my hardy hole, a trick I stole from one of my instructors who uses a similar setup when he is out demoing somewhere.  I mainly use it, though, for when I'm doing some grinding outside my shop, holds things in place while I work and is at a better working height for that than my post vise.  

You can pull the base off any rotatable vise and install a bolt for a similar vise. There are models that came that way but you CAN make one if you wish.

Very handy tool to have on the shelf.

Frosty the Lucky.