Michael
I think that is one of the bigger ones.
There are several different versions and sizes of these devices. From memory I'm fairly sure there are four different base designs and three, maybe four sizes.
Types 0, 1 and 2 certainly out there. I've seen a reference that type 2 is 5 1/2 inches , 140 mm jaw width. The common one seems to be 3 inches (nom), 70 mm, jaw width, allegedly size 0. I'd expect type 1 to be around 4 inches, 100 mm, jaw width. There may be a type 4 of 6 1/2 inches, 170 mm, jaw width but the data given was less than clear.
Opening always seems to be about 10 mm less than jaw width.
The bigger one(s) have four short mounting slots, one at each corner, pointing sideways.
The small ones have a single short slot at the front centre and either two long slots angled backwards from the middle(ish) giving a Y formation or two short sideways slots right at the rear.
Also a variant with the short sideways slots a little forward of the rear of the base. Only seen one picture with no size indication.
I got curious after finding mine and spent some quality Google time.
Clive