Does anyone know the purpose of this tool?  The holes are threaded.

Fixture for flaring tubing , one of pieces needed

One of two pieces needed, the other being the actual flaring tool.  Gooogle "flaring tool" for examples.

Are you sure they're threaded?  They're often ridged - look like threads at first glance, but not spiral - to improve the grip on the tubing.

like the others have said part of a flaring tool, the part you are missing is on the top  left