For me, one of the most fascinating part of a machined pen is the mechanism. But before we dive into the different types, let's look at the one ubiquitous part you’ll find in almost all of them.

The Spring

So, why is a spring actually required?

I like to think of a pen as a simple state machine. It has two distinct states: Retracted (tip inside) and Extended (tip outside). Moving between these two states requires an action: engaging or disengaging the mechanism.

Let’s break down the role the spring plays in each step :

• State: Retracted (Rest) The spring sits on the shoulder of the refill. Even at rest, there is a little bit of tension keeping the refill from rattling or slipping.
• Action: Engage When you click or twist, the spring compresses. Since the spring is wider than the pen tip opening, it can't escape. Instead, it pushes back against the refill, absorbing and storing that energy.
• State: Extended (Active) Now, that energy is stored. The mechanism is locking the refill down, while the compressed spring is constantly trying to push it back up. This tension is what keeps the tip firm while you write.
• Action: Disengage This is where the magic happens. The mechanism unlocks, but it doesn't actually pull the refill back. It just gets out of the way. The spring releases its stored energy and physically pushes the refill back up by the shoulder.

Now that we understand the spring's job, let’s explore some simple but amazing mechanisms. (Note: From now on, I won't count the spring as a "custom part" of the mechanism, even though some makers—like Magnus—do craft their own custom titanium springs!)

Now, back to mechs !

Mech 1 - Autmog Twist :

The Minimalist: Autmog Twist

How the Mechanism Works This is arguably one of the simplest mechanisms in existence. It consists of just two main custom parts: the pen body and the mechanism itself. You don’t even need tools to take it apart.

• To Engage: When you screw the mechanism down (clockwise), it physically pushes the refill forward, compressing the spring and extending the tip.
• To Disengage: You simply reverse the action. As you twist counter-clockwise, the mechanism backs off. This allows the spring to release its stored energy and push the refill back inside.