Monteverde Mini Ink Cartridge Converter

Does what you need. No frills but basic function.

Bought for Kaweco...

Bought these because the ones I picked up years ago fit my Kaweco Sports really well (and they're a bit cheaper than the fancy Kaweco ones). The not sure what has changed, but the tip is a little too big for the ink feed to grab. I got crafty and used a lighter to melt them slightly and press them in firmly to make a more ink-tight fit, and that worked well. If you're here for the same reason, and you're not so inclined to do all that to save the $3, probably just stick to the Kaweco brand converter, cuz they're just the teensiest bit too loose to latch without alteration.

I'm satisfied with it, but it could be improved.

I got this converter for using with a J. Herbin rollerball pen. It works well enough, and I don't have any real complaints, but if I were the one who designed it, I think I would have made the piston a little sturdier. It fills with ink as well as I'd want it to, but the piston itself is ever so slightly crooked, and the soft-feeling plastic seems like it might eventually break.