Chris23:
Hats off to you for being a good sport about my reply to your post.
As for vise jaw width being "non standard" (at least by US practice), it may well be a metric jaw width. Your vise looks as though it were designed for mounting on a swivel base, given the shape of the base flange and bolt hole locations. The design follows more of the English or European machinist bench vise design rather than US designs.
I agree with the posts about leg vises vs machinist vises. I have both. The leg vise is for smithing work such as hot bending, chisel/splitting work, hot rasping and hot twisting to name a few uses. As noted, the jaws do not close parallel, so getting a real good "bite" on work for things like tapping, filing, chipping (done cold with a hammer and cold chisel or cape chisel) you will find the work will move in the jaws. The leg vises are great for smithing, but really are not so good for "cold
work" or finer machinist work. I also learned many years ago that when I tried to turn a frozen nut off a bolt held in the leg vise, it popped out of the jaws- the hex flats having what amounted to "line contact" with the non-parallel jaws. Any movement that wiggled the hex flats in the jaws resulted in the nut or bolt head climbing right up out of the jaws. For smithing work, the tendency is to drive the work downwards more often than not. Since the jaws are non-parallel with the larger opening at the top, driving work downward in a leg vise will tend (at least in theory) to wedge it tighter in the jaws. Jobs like filing work will tend to pull the work up and out of the jaws.
A type of smithing that comes in handy, for which a leg vise is ideal is "hot rasping". Using a hoof rasp on red-hot steel, a surprisingly quick amount of shaping can be done. You would not want to put red hot steel in a good machinist vise with hardened steel jaw plates. A lot of smiths get worn hoof rasps from farriers if they do not have them already. The force of hot rasping is usually not sufficient, nor is it done long enough to rock or pull the work up out of the jaws of a leg vise.
My leg vise is mounted on its own stand. I had a chunk of 4" scrap steel pipe, a large "blind" pipe flange ( a disc of steel with the bolt circle drilled in it, but no hole for connection to a pipe), and some 3/4" steel plate pieces that were about 12" x 12". I combined these pieces to make a stand for my leg vise. The 4" pipe is capped with a 12" x 12" x 3/4" steel plate at each end, making it a column. The top plate is drilled & tapped for bolts to mount the leg vise. The bottom plate is drilled for 3/4" diameter bolts. The blind flange is drilled & tapped 3/4"-10 UNC so that the bottom plate of the column bolts solidly onto it. The bottom end of the vise leg (which will usually have a collar on it) fits into a "socket"- a piece of 1" steel stock drilled for a good fit with the bottom of the vise leg. After the vise was bolted solidly to the top plate, I used the leg to position that "socket" piece and welded it to the blind flange. The result is the leg vise is married solidly to the stand. I move the vise and its stand with a hand truck or pick it up with my tractor (boom pole on the 3 point hitch) and put the vise/stand where I want it.
A leg vise's jaws are designed for accessability and work you could not hold handily or effectively in a regular machinist vise will often be better in a leg vise. Smithing work is often on longer pieces of work with some bends in them, while the machinist vise is more for smaller work.
Each vise has its uses. There is some overlap in what each vise can do, but for smithing and hot work, use the leg vise.