Gem-setter’s tool

The answer to the last mystery object competition is a gem-setter’s tool. The point on the left centres the tool on the hole where the stone is to be set. Two adjustable cutters are held in place by the four screws behind the point. The tool is held by its pivot on the left in an upright drilling stock, and rotated with a bow. The cutting bits carve a lip of metal around the hole, which is pushed down over the gem with another tool to set it.