New one to me, also. I've got at lest 20 pairs of parallel-jaw pliers, some with very specialized jaws, but nothing close to this. I wonder if they were used to first grip, and then to pull or tension something by using the handles as a lever, pivoting on the rounded "heel" of the side piece? Plating suggests factory-built, to me. Even today, you can request pliers with screws (so jaws are removable), and buy unplated, unhardened jaws - or at least you could about 2-1/2 years ago, the last time that I did so. I machined a pair of very specialized jaws from aluminum, figuring that once they were proven to work, we'd get several sets made up by some shop with CNC equipment, in steel, and then get them heat-treated and plated to suit. They DID work, but I've retired and don't know what has happened since.