Cartridge Roller ball System by Schmidt.
This is the same great system as the regular cartridge rollerball system, except now with a metal tip (chrome plating) to better match your pens! Now convert your fountain pen into a rollerball that will accept standard fountain pen inks, with this innovative system. Works with standard fountain pen ink cartridges and converters.
Most #5 fountain pen kits (Jr Statesman, Jr Retro, some Jr II (Dayacom) and others) will require chasing the threads with a M6.4 x 5 tap. May not be suitable for all pen kits. (Will not be compatible with Jr rollerballs, or #6 fountain pen nib sections.)
The Cartridge Rollerball system has a 0.7mm TC ball. and comes complete with a snap cap.