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Flexible Nib Factory ZT5E Review

Posted in Fountain Pens, and Reviews

DISCLAIMER UPDATE (6/24/22): TWSBI and Narwhal have released a joint statement which I cover in my most recent TWSBIgate post. While not completely satisfied with TWSBI’s response to the situation, I no longer feel the need to dissuade people from purchasing their products.

DISCLAIMER (5/1/22): Since writing this post, TWSBI has been involved in some unsavory actions, and I am currently boycotting them. For more information, refer to the #twsbigate tag page.

In late February, I saw a post on Goulet Nation where someone was showing off a new nib. But this wasn’t any old nib, it was the Flexible Nib Factory ZT5E. Or, in English, a custom feed and housing to allow the use of a Zebra G dip nib in a TWSBI 580 series pen. Since Zebra G nibs are what first sparked my love of flex nibs, I immediately purchased a ZT5E.

Before I dive into the actual review, I want to make it clear that as far as manufacturing and production, I think the ZT5E is top-notch. My critique should be read with the awareness that this is a dip nib housed in a fountain pen. Flexible Nib Factory has provided a way to fit a square peg in a round hole, basically.

I think it’s worth noting that these won’t fit in a Diamond Mini. While the Mini is based off of the 580, it’s not technically a 580. The Mini cap is a couple of millimeters shorter than the 580 cap, and the Zebra G nib is long enough that it simply won’t allow the cap to close.

It Works, Mostly…

Yes, it writes. Yes, it flexes beautifully. However, it’s very picky about which ink you use. And here’s where it gets complicated.

When I first inked up this nib — that reads oddly, as you ink up a pen, not a nib, but it’s how I will refer to things — I used Sailor Ink Studio 173. The nib had major trouble keeping up with my regular writing speed. I think I write slightly faster than average, but I don’t have a lot to compare to, so I could be wrong about that. Up strokes, especially, were often almost non-existent.

showing difficulty when used with Sailor Ink Studio 173
Notice all the upstrokes that are thin or non-existent.

Jim’s theory is that it could be ink starvation — not enough ink getting to the tip — because the feed ends so far from the tip of the nib.

showing the space between top of feed and tip of nib

My theory, however, is that this nib works better with more viscous inks — which would make sense as it’s a dip nib, and dip ink is more viscous. However, I’m not going to run the risk of ruining a beloved TWSBI to properly test out that theory.

Instead, I inked it up with Rohrer & Klingner SketchINK Lotte. The SketchINK series is a teensy bit more viscous than standard fountain pen ink, maybe because it has nano pigments. It’s also waterproof, which means it has to have some kind of additive, that could be contributing to the slight viscosity difference. Whatever the reason, the slight difference in ink made a huge difference in performance.

I didn’t have a single problem with writing performance. The nib kept up perfectly with my writing, and I got some light flex on my downstrokes.

Notice the lack of missing upstrokes. And the bloop wasn’t that big, it spread when I plopped down a blotting paper to soak it up.

… But There are Some Quirks


The biggest quirk is that this nib has a tendency to bloop ink if you hold it in a writing position without writing for more than a couple of seconds. You can actually watch the drop of ink form, if you’re paying attention. And after the drop forms, it takes a bit of back and forth (tilting the pen up so it will drain, then going back to writing) to get it to go away and stop. But, if you write consistently, and hold it nib up the moment you stop, it’s fine.

Jim and I both feel this is likely because of the oversize breather hole. That hole is, naturally, directly over the feed channel, which, in this case, is widened. So there is a large area with no ink regulation. Of course, we could be completely wrong about this theory, but it makes sense.

showing the large breather hole

Nib Seating

Another quirk is that if you disassemble the nib unit — whether to swap out the nib or to clean it — you need to reinsert the nib first, then the feed. This is because you must ensure you’ve pushed the nib in fully. The G on the nib should be touching the housing.

showing how the nib should look when fully seated
It was hard to capture in a photo, but you can see how the G touches the housing.

If you don’t do this, the cap won’t close fully. The nib has such a small clearance, that it must be fully seated for the assembly to work.

showing how the cap doesn't close if the nib isn't fully seated
That’s a lot of leftover space just because I didn’t get the nib fully seated.

Loose(?) Sections

And finally, even with the ZT5E screwed in all the way, the TWSBI section can still turn around. It seems to tighten all the way with my 580AL Emerald — that section doesn’t turn. But the 580 and 580ALR both still turn freely. I wonder if it’s because the ZT5E doesn’t have the little rubber O ring and “fins” that the TWSBI housing has. Not an issue, just weird.

showing the differences between the ZT5E and the standard TWSBI nib
Notice the “fins” — or ridges — on the TWSBI nib under the O Ring.

Final Thoughts

Overall, I’m not upset with this nib, but it’s a novelty, not a standout flex mod. At $42, it won’t break the bank, but be aware that you aren’t getting a top-of-the-line flex nib. I think, with practice, I could probably get to a point where I don’t have to worry about bloops — assuming I’m using the right ink. I just don’t know how much use this particular nib will actually get, given that I have other, more user-friendly, flex nibs.

What do you think of this nib? Do you have one? If so, do you like it? If not, are you interested in it? Do you have any theories about the blooping issue? Let me know in the comments, I love hearing from you.

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