The Uniball Signo RT Gel mini Hack


"I’d purchased a 4-pack of Pilot G2 mini 0.5mm
pens for pocket-ability, but found the ink bled a bit too much through
the thin Moleskine pages, so I picked up a 4 pack of Uniball Signo RT
Gel 0.38mm pens. The thinner 0.38mm gel pens work well with Moleskine
paper because the line is thin and quick drying.

This weekend I was looking at the Uniball Signo and G2 Mini, when I
wondered if I could hack the Uniball 0.38mm refill to work in a G2 mini
pen body. When I took the two pens apart, I realized it could be done,
with a flick of a utility knife to trim the Signo’s cartridge down to

In the spirit of DIY, I gave it a try. The G2 mini to Uniball Signo
mini conversion worked so well, I’ve decided to to share the easy
conversion process with other Uniball Signo fans out there.."

Mike Rohde


13 thoughts on “The Uniball Signo RT Gel mini Hack

  1. It’s strange. I’ve seen several complaints about Pilot G-2 ink bleeding through Moleskine pages. Yet I write on pocket ruled Moleskines with Pilot G-2 05 pens all the time, and never have this problem.

    Still, 0.38 mm sounds cool–I like a fine line–and the ink sounds superior, given Mike Shea’s experiment. So I’m glad Mike Rohde figured out how to put it in a G2 mini body.

  2. Without a dought the signo rt .38 is the best thing that has happened to a Moleskine. For a nicer pen body I have found they fit in a Waterman or an ACME pen body as well.

  3. Hey, I stumbled across this site looking for the Signo .38s, but I tried the modification you suggested with my Sensa. I used the spring from the Signo body because the Sensa spring was too small, but now the cartridge retracts – by itself – into the body of the pen.

    Is the spring too big? Did I cut the cartridge too short? I was using Parker gel refills but I hate them; far too big.

    I really, really want to be able to use the .38 cartridge in the Sensa. I hold my pen too tightly to be comfortable with a normal, hardbodied pen.

  4. After reading this article a couple months ago, I got some of these Signo RT 0.38 pens, and they are GREAT. The only trouble is they run out of ink quickly! I do tend to use them more than other pens – but I think there is just very little ink in there. And forget about refills – they cost the same as a new pen!

    They really are hard to find – the only places I have found them are:
    1. ($1.50 each, free shipping on orders over $25)
    2. ($1.76 each + $3.95 shipping)
    3. (item #479588, $16.79/dozen + $7.95 shipping)

    So if you’re buying 2 dozen, the totals are
    jetpens: $36.00
    discountofficesupplies: $46.19
    staples: $41.53

  5. i use the .38 signo’s exclusively for a few years now. in the interest in minimizing waste, i’d like to buy refills from now on. i cannot find them. please post links here

  6. Just wanted to add that the UniBall Signo “.38 special” is indeed the superior Moleskine pen. I have been testing different inks and leads for the past few months, and that one was the clear champion. fairly waterproof and you can still use both sides of the page.

    we all know that ANY ink will show through the super-thin paper, but this one seems to produce minimal shadowing. if you haven’t tried the Uni .38, it’s an inexpensive experiment to find out how great it works. I like the blue inks myself on the creamy paper.


  7. It’s worth noting that I’ve been able to successfully swap the tip of the .38 cartridge with that of one of the larger .7 or .5 ones. The problem with the .38 is that the internal tube of the cartridge is much narrower (2.5mm versus 4.5mm on the .5), which means an ink volume of 344 microliters versus 1113 microliters, assuming about 7cm of ink in either cartridge. That means the larger nibbed cartridges have over three times the capacity of the .38’s! All you have to do is remove the nib from a .38 and a .5/.7 with a pair of pliers (twist; they come off easily), apply light pressure on the opposite end to push the ink slightly out of the cartridge (so that no air bubbles get trapped), and push the new nib back in.

    This also means that the nib can be reused, and you only have to buy new cartridges in the larger sizes… until your nib wears out.

  8. I found a bunch of G2 .38 pens at a store in San Antonio, an Air Force BX to be specific. I should go back and stock up.

    I never saw the .38 before, only the .5. Too bad they were out of red, the bright in and strong, fine lines make for fantastic copy editing.

    And, over the years, I found the ink in the G-2s to be very smooth and damn near indestructable. I accidentally washed a Moleskine in a washing machine. And, whike the notebook swelled to twice it’s original size, none of the red G-2 in ran or bled. It was all perfectly readable.

    Now, as for how I can wash a pair of shorts with a notebook in the pocket is beyond me.

    I thought I was nerdy about pens and my beloved Moleskines, you guys take the nerdiness cake. And I mean that in the best possible way.

  9. Hola! I’ve cut and installed cartridges in my Pilot G-2 Mini for some time (just used Pilot Q7 cartridges and they work OK) and am curious if anyone has injected ink into a used cartridge. It seems to me it’s a possible way to refill…just pull off the tip and the cap, fill with ink, and replace the tip and cap on the opposite ends. Any thoughts?

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