Vintage Bergeon crystal lift tool. These are the tools that watchmakers and watch repair people use to install acrylic or plastic watch crystals easily and safely without damaging the delicate crystals or the watch bezel. The jaws open all the way to 45 mm so they are appropriate for even today’s larger sized watches.
I’ve just replaced the rubber o-ring that provides the counter tension for the jaws, but just so you know, if you ever have trouble in the future, it’s likely a $1 repair. This thing is built solid and the mechanism itself is simple… translation: it’ll work well and last forever. You could clean this up to look a little nicer or use it just as is, your choice.