It has just come to my attention that the 8mm Metallo pen kit may be in the process of being phased out. PSI is presently selling these kits at closeout sale prices (50% off!). At this point I'm not sure if the kit will be available from another vendor in the future. If you want to assemble one of these 8mm Metallo kits I would recommend you purchase the pen kits before purchasing blanks from this store.
If I can't identify a pen kit that is compatible with the Metallo blanks in this store I will port them over to other pen kits that can play nice with the 3D printing design rules. If you have any suggestions for a favorite pen kit of yours let me know.