RADIN G2 — The Small Part Behind a Big Change

When I first shared RADIN on r/machinedpens, many of the comments asked the same question: "Can it take a G2 refill?"

The original RADIN used a Cross-type refill, and there was nothing wrong with it. But those comments taught me that in the machined pen community, the most preferred refill — often a requirement — is the Parker-style G2.

Those comments became the starting point for RADIN G2. The goal was clear: make RADIN take a G2 refill without changing its dimensions, its form or its character.

It sounded like a simple change. Once I started, it became clear that it wasn't.

The Problem: A Refill Without Threads

A Cross-type refill has a thread at its end. In the original RADIN, the refill passes through the twist mechanism and screws into it. When the mechanism moves forward, the refill moves forward; when it moves back, the refill is pulled back with it.

The Parker G2 refill had no thread, so the same mechanism could not be used.

The first step was to find a twist mechanism suited to the G2 refill. I found one and sourced it from the Netherlands. But that created a new problem: the mechanism would not fit the existing RADIN body.

The Solution: A Brass Adapter

The part that makes RADIN G2 possible is a small brass adapter hidden inside the grip section.

This adapter does three things at once:

• It lets the G2 refill pass through it.
• One end screws into the knurled grip section.
• The other end screws into the twist mechanism.

That meant cutting two different threads, in two different sizes and pitches, on one tiny part. Because the tolerances are very tight and the walls are very thin, machining it on a manual lathe demanded far more care and skill than the rest of the pen. The hardest part of RADIN G2 turned out to be its smallest one.

Along with the adapter, the inside of the grip section changed too. Internally it is longer and different from the original RADIN. From the outside, none of this is visible.

The Spring That Brings It Back

A refill without threads has one more consequence.

In the original RADIN, the refill is screwed to the mechanism, so when the mechanism retracts, the refill retracts with it. In G2, the mechanism can only push the refill forward; it cannot pull it back.

So I added a steel spring that the original RADIN doesn't have. When you twist the mechanism back to close the pen, this spring pushes the tip back inside.

The Only Visible Difference: The Window

All these changes leave just one visible trace on the outside: the position of the mechanism window.

Because the Cross refill passes through the mechanism, the mechanism's length doesn't add to the pen's overall length. With G2, most of the mechanism sits beyond the refill. That places the twist mechanism higher, and the window that shows the twist actuator moved up by about 10 mm.

The length (134 mm), diameter (12 mm), knurled grip and overall form stayed the same. Arguably, the window's new position is even more striking.

Listening to the Community

RADIN G2 is an example of a design evolving together with the people who use it. The request was simple: "Make it take a G2." Meeting it took a new mechanism, a custom adapter, a redesigned inner body and a spring — none of which you can see from the outside.

Perhaps that is exactly what a good mechanical solution does: it shows the user only the result.

The pens in this story: RADIN G2 Brass and RADIN G2 Aluminum.

RADIN G2 — made one at a time on a manual lathe in İznik, Türkiye.