One side says "PREMA 100 PATENTED". Both pieces at each end pivot on a pin.
If you imagine a barrel nut
(https://images-na.ssl-images-amazon.com/images/I/61PIit7JwjL._SY450_.jpg)
but with an untapped hole, resting in the rounded area at the bridge between the two blocks, with a bolt running up from a machine table's slots, would you have an auto-adjust clamp to hold work on that machine table?
Not sure about this - just a thought.
At first I was thinking maybe something to do with holding piping, but the three rounded parts are all the same size.
Prema makes tire repair tools and chemicals. Possibly part of a bead breaker tool???
Chain stretcher? part of it looks like part of a chain sprocket?