Gel ink refills from Ohto that can fit all the Ohto Liberty pens such as the Ohto Fine, Orca and more. These refills are the same size as the C-30X (i.e. C-305, C-307, C-310 etc) Ceramic Roller Ball series and are interchangeable. The G-30X series has gel based ink instead of the water based ink of the C-30X line. 0.5 mm, 0.7 mm and 1.0 mm sizes available.
The G-307 gel ink cartridge is the way to go! Very smooth and never skips like
the C-307 cartridges have a tendency to do. Might be the perfect ink cartridge,
and I've been searching for that for a long time. The G-307 is smooth in a
controlled way for a .7mm cartridge, and doesn't get sloppy the way the Parker
Gel Ink refills can get. Only issue might be how long they last and whether or
not they begin to write differently towards the end of their capacity. Will keep
you posted. Makes my Orcas the perfect pens!