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.