This 3D Printers Brass Nozzle 0.4mm is a fully functional metal extruder, backwards compatible with all 3d printer is basically a high-end dual extrusion system, using two interchangeable nozzles.

You can use two different wires in the same print job and be able to do their own level, and regardless of which side printing heat will not appear other double extruder 3D printer rubs and other common problems.