Odd "tool"

[MplsJeff]

One side says "PREMA 100 PATENTED". Both pieces at each end pivot on a pin.

[Bill Houghton]

If you imagine a barrel nut

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.

[MplsJeff]

 At first I was thinking maybe something to do with holding piping, but the three rounded parts are all the same size.

[amecks]

Prema makes tire repair tools and chemicals.  Possibly part of a bead breaker tool???

[oldgoaly]

Chain stretcher? part of it looks like part of a chain sprocket?