I can't be 100% sure as the pic gets too grainy when I enlarge it, but it looks like a standard I beam clamp, and they don't roll horizontally (unless you push them when they're loose) - basically just a big jaw that winds shut but overlaps the bottom edge of the beam. I bet a pint that it go put on, slid along, then someone had to do something silly in order to tighten the jaw shut!