This is a connector for the deflector dish in 1/350 scale. It's to help in converting your Round2 TOS Enterprise into a Scout/Destroyer/Hermes/Ptolemy class. This one is based on the Franz Joseph design in the Star Fleet Technical Manual. It replaces the lower dome on the kit completely. It fits perfectly with the kit's dish.
I also make a more detailed version based on fan concept work
available here.