The Ultimaker 3 and the Ultimaker S5 are compatible with the entire range of available print cores, including AA 0.25, AA 0.4, AA 0.8, BB 0.4, and BB 0.8.
Older generation print cores include a nozzle ring, which must be removed before use with the Ultimaker S5. Failing to remove the nozzle ring for use with the Ultimaker S5 may prevent the print head fan bracket from closing properly. This is because the nozzle cover on the Ultimaker S5 has been redesigned since the Ultimaker 3, creating a tighter seal around the print cores, with less space inside of the print head.
If you want to use the same print core with the Ultimaker 3 later, the nozzle ring does not have to be replaced. After extensive testing, we have determined that the silicone nozzle rings are unnecessary, and have removed them from all new generation print cores.
Caution: Using a print core that has a nozzle ring on the Ultimaker S5 may cause the fan bracket to fall open during printing, which can cause damage to your printer.
Note: It is also important that the outside surface of the nozzle is clean. Before inserting a used print core in the Ultimaker S5, ensure that there is no nozzle ring or filament residue on the print core.