The hardcore 4 is a 3D Solex retrofitted Print Core for the Ultimaker 3 that allows the changing of nozzle tips. It comes with 4 different sized nozzles that can be changed by unscrewing and re-screwing on the new nozzle size. The heatsink maybe red or gold.
Users who are changing nozzles with this system should print this nozzle changing tool for best results.
This is a 3rd party print core and not supported by Ultimaker, users should consider this kit for advanced to expert use only.