Picked this up today at the antique store, trying to find out some information about it. The knob at the front adjusts the main screw, and when you're close you turn the handle about 90 degrees to clamp it down. I'm not sure what the contraption on the back does. The screw is stuck, so I'll have to try to get everything freed and mess with it more tomorrow. I've never seen such a thing so it came home with me. I can't seem to find anything on the internet, hoping to find out if this is a factory made vise or someone modified it along the way. Either way, I think it's neat and could be useful after some TLC.