Gentlemen and Ladies - Thanks to those who identified properly the tool I asked about. It is a black tool, heavy cast steel, that looks like very high leverage pliers. In the jaws there are two circular inset pieces 10 mm diameter and concave. They are offset wrt each other by more than a mm, so it closes buck-toothed.
If you find such a tool, it is a nice thing to have. It is for nipping off the ends of spokes that protrude through the nipple and would otherwise jeopardize your tubes. One of the faces engages the nipple, and the overshot one nips off the spoke end.
Besides, most of your friends will never figure out what it is for....
thanks again, and happy holidays.
harvey sachs