Mark One, our best-selling retractable pen with a satisfying-as-heck click mechanism, ships with a branded version of the Schmidt P8126 rollerball ink refill. This refill is beloved by many, including us, which is why it is the default refill in Mark One. However, if this specific refill does not suit your preferences, you are in luck, as there are tons of compatible refills. Below, you will find information about compatible refills for Mark One, and some of our top recommendations. Or, just watch the video:

The world of pen refills can be a little confusing, especially to a newcomer, so we wanted to create this guide to give an overview of some of the ink refill options for Mark One. Refills for Mark One come in three categories: rollerball, gel, and ballpoint. All three types are essentially the same mechanism: a ball in the tip that is coated in ink and rolled along the page. The difference between the three is how the ink is formulated. 

Rollerball refills use a liquid ink that is a dye dissolved in water, similar to fountain pen inks. As such, the ink flows freely and requires very little pressure. But the paper choice is more critical because lower quality papers will exhibit feathering or bleed through.

Gel refills use an ink that consists of a pigment suspended in a water-based gel. They are known for a lubricated, smooth writing experience, but can sometimes skip more than rollerball or ballpoint, and the drying time is longer than ballpoints. 

Ballpoint refills use an oil based ink, a mixture of dyes, alcohols and fatty acids. The ink is thick, so it works well on lower quality papers, but it requires the most pressure of the three to write. The lines are generally not as dark as rollerball or gel, but they are quick drying and waterproof. 

Below are some refills from each category that we have personally used and liked. All have been tested and confirmed to be compatible with Mark One.

Rollerball Refills

Rollerball refills are most akin to a fountain pen: smooth, liquid ink that hardly takes any pressure to apply to the page. Our refills are made by Schmidt, a German company that has been making writing instruments for over 85 years. Their P8126 refill is what we include in the Mark One, but they make this refill in 4 different line widths: P8125 (0.5 mm), P8126 (0.6 mm), P8127 (0.7 mm) and P8120 (1.0 mm). Even though the thinnest tip, P8125, is listed in their product catalog, I have yet to see it for sale anywhere. It might be something that needs to be special ordered in large quantities. But the other three options are readily available:

Schmidt P8126 (Studio Neat | Jet Pens)
The refill that comes with the Mark One. We sell a branded version in blue and black ink, and Jet Pens has green and red as well.

Schmidt P8127 (Amazon)
A slighter thicker line, but otherwise the same. Offered in black, blue, red, and green.

Schmidt P8120 (Amazon)
A super thick line. Blue and black ink options available.

Gel Refills

Gel refills are a great option if you are looking for a smooth writing experience, where the pen feels like it’s gliding over the paper. Gel pens are notorious for sometimes skipping during writing, but the refills below are tested and work well, and are well regarded by pen nerds. 

Meister by Point (Jet Pens)
A very nice gel refill, with a needlepoint tip. A smooth, consistent line.

OHTO PG-M05NO Ceramic (Jet Pens | Amazon)
Another solid needlepoint gel refill, though quite expensive. Good line consistency.

OHTO PG-105NP Flash Dry (Jet Pens | Amazon)
A cheaper version of the refill above. Not quite as reliable as the ceramic version, especially on the first stoke.

Monteverde P41 (Amazon)
Another popular needlepoint gel option. Available in black and blue.

Kaco G2 (Amazon)
Another solid gel option, especially if you went a regular conical tip instead of a needlepoint. In black and blue.

Kaweco Sport Gel Roller (Amazon)
The thickest gel refill tested, by far. If that’s what you’re after, this one is for you.

Ballpoint Refills

Ballpoint refills trade writing pleasure for robustness. They require the most pressure to get a consistent line, but they work well on any paper you throw at them, and dry quickly.

Schmidt easyFLOW 9000 (Jet Pens | Amazon)
Schmidt claims this is like a hybrid between a ballpoint and a rollerball. It would be a good option if the P8126 is a little too smooth for you and you’d prefer slightly more resistance. Available in Fine (F) and Medium (M).

Unibene Ballpoint (Amazon)
A solid ballpoint option, and my wife’s preferred refill in the Mark One. Quite cheap, less than $1 per refill, and comes in black and blue.

Uni Jetstream SXR-600 (Jet Pens | Amazon)
A very popular ballpoint refill option. This is the pick if you prefer a very thin line. Comes in 0.38 mm, 0.5 mm, and 0.7 mm.

---

A Note About “Parker Style” Refills

“Parker Style” refills are sometimes referred to as G2 refills, which is confusing because they are not compatible with Pilot G2 pens. However, Parker Style refills are easy to spot because they have this toothy looking plastic part at the end of the refill:

In Parker pens, this plastic bit actually engages with the teeth of the mechanism, but in Mark One that bit is not needed for our custom mechanism, so it is simply ignored.

You can put a Parker Style refill straight into a Mark One, and it will fit and work perfectly fine. However, we recommend one minor modification. Parker refills are actually every-so-slightly longer than a Schmidt refill, due to the little nub that protrudes out of the back end. When engaged, the tip of the refill sticks out of the Mark One slightly more than ideal. The fix, however, is easy: simplify slice off that little nub. Any blade will do the trick.

Here is what the refill looks like, before and after slicing that little piece off the back end:

---

A Note About the Spring

The spring that is included with Mark One will certainly work with any refill you swap into the pen, however if the neck is a different length than on the Schmidt P8126, it will affect how the click feels. Feel free to experiment with other springs if you are not happy with the feel, perhaps harvesting one from a different pen.

---

When we were first getting into the world of pens, this refill guide from Well Appointed Desk was immensely helpful. It’s a great place to start if you want to see a list of compatible refills. This guide from Jet Pens is also a good reference.

We hope this guide is a useful primer for the world of ink refills for Mark One. As always, email us with any questions!