A Pentel Energel refill might be another possibility, once you trim it to fit.

That Rotring uses a standard Parker-Style G2, yes?

I realize the Pilot G2 in an entirely different pen and refill, but I managed to cut the end off one and put it in my Kaweco Sport (sans spring), and it worked just fine! (See my other reply in the thread for the caveat about the grease-plug.)

Pilot G2 comes in a ton of great colors. I’d bet money they have the dark green ink you want in a gel.

Just hacked a green Pentel Energel refill to fit inside my Kaweco Sport “Raw Aluminium!” It seems to fit perfectly now. I took out the spring, which the pen does not truly need unless you are using a Parker-style G2.

Not to be too confusing (sorry!), but I also got this to work with a Pilot “G2” refill, which, as noted above, is notnotnot the same as the Parker-style G2. But I did get it to work, with a caveat.

I had purchased a multi-pack of the Pilot G2 pens in assorted colors. There was one that was truly horrible, a greyish ink I could not ever imagine using, and that is the refill I experimented with.

The Pilot G2 refills seem to have a “grease-plug” in the body, and a plastic cap on the end (matching the color of the ink? This one was grey . . .) once I cut the pen to fit, the only thing holding the ink in was the grease-plug, which did not leave me feeling confident. It “worked,” which means you can get any colour you can find in a Pilot G2 to work in the Kaweco Sport, but I’d be very careful with this. I think I may try a bit of rubber cement or white glue in the end of this refill before I trust it, or one like it in green, which is what I was after.

It was nice, managing to hack a $2.00 pen I can buy in Office Depot, rather than ordering a $5.00 refill that would have to be shipped here by Amazon!

I’m new to the pen world, but have instantly become hooked. I’ve made several purchases from Jet Pens and Van Ness, resulting in my favorite pen so far, a Rotring 600. Now to find the perfect refill for it. I’ve got a couple of Monteverde refills on the way, but ultimately I’m in search of the perfect dark green ink. Dare I ask… would it be possible to fill a Monteverde refill with fountain pen ink? Is the viscosity (consistency) different? Would it work in a gel cartridge? Robert Oster has some great ink that I’d love to have in my Rotring….

Is there an accepted hack for using a Parker/G2 refill in a pen body that normally takes a Pilot G2/Euro-format refill?

Thanks in advance for any suggestions or an explanation as to why this is not practicable.

Monteverde makes Montblanc-specific rollerball refills. You can find them on their website.