Until last weekend's yard sale, I never knew Ridgid made pipe wrenches this small. This one will accommodate up to 3/8" pipe, but you'd sure have to be strong to get much grunt on it. As you can see, this one's not the traditional Ridgid color, but is painted gold - I'm wondering if it was some kind of service award.
To my surprise, Ridgid still lists this size in its catalog, where it's listed as "nominal 6 inch" size. With the jaws all the way open, it is indeed six inches long. Maybe there are applications for it, but it's hard to imagine there many places it would be useful.