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.
After trying this 0.5 black Gel refill for the Ohto pen it is now my favorite.
Until I discovered Jetpens I had been using the Uni-ball 207 0.5 (micro)
cartridges (scavenged from 207 RT pen donors) in my Ohto pens. The G-305
produces a slightly darker black than the Uni 207's. Otherwise the performance
is similar and the sealed metal cartridge is a plus compared to the plastic
207's. The only reason I would not use these would be cost as you can get a two
pack of the Uni 207 Rt's for about $3 vs $5 each for the Ohto Gels.