Castle Neu 1717 Bearings Size

Hi all, I would like to change the bearings of my 1717 so to use hybrid ones (steel + ceramic) as I've done for the 1520.

Does anybody knows the size of such bearings ? I have the 1717 with a 5mm shaft, but I noticed that the shaft reduction from 6 to 5 is just for the outer part of the shaft, while the inner remains of 6 mm.

Thanks, Andrea.