Micro-Adjust CTS Deployant Clasp — The Technical Side

The problem worth solving

One of the most familiar and useful features of a traditional leather strap is also one of the simplest: The row of sizing holes. Those holes do more than accommodate different wrist sizes. They also allow the wearer to make quick adjustments throughout the day, whether for comfort, temperature or activity.

That matters more than most people realise. Wrist sizes are not constant. It changes with heat, movement, humidity, and even how long a watch has been worn. A strap that feels perfect in the morning can feel tight and irritating by the afternoon, while one that feels comfortable at rest can start to shift around too much during activity.

On a rubber strap fitted to a deployant clasp, solving that same comfort problem is much less straightforward. Unlike a traditional strap, the length of a cut-to-size rubber strap is fixed once it has been trimmed. On our existing system, there was already a form of fine adjustment, but it still required a separate tool. We were confident in the comfort, fit and security of the system as a whole, but we also knew that when the fit was not quite right, that mismatch was often felt more immediately on rubber than on leather.

So the problem was clear: How could we bring truly practical micro-adjustment to a rubber strap clasp in a way that felt intuitive, secure and natural in daily wear?

What already existed, and why it was not enough

We did not start from a blank page. There were already solutions in the broader world of straps and bracelets, and each taught us something.

Traditional leather and fabric straps, for example, rely on the softness and flexibility of the material itself. Adjustment is made possible by holes, slots or woven structures that can withstand repeated engagement and remain functional. Metal bracelets, by contrast, can take advantage of being made almost entirely from rigid components. That opens the door to finely-machined adjustment systems with precise tolerances and locking positions.

Rubber straps with deployant clasps occupy a less forgiving middle ground. The strap body is semi-soft, but the clasp mechanism is rigid, compact, and constrained by very limited space. That combination makes it difficult to borrow solutions directly from either side. Methods that work beautifully on leather or fabric often depend on material behaviour that rubber straps do not share. Mechanisms designed for all-metal systems, meanwhile, usually rely on construction methods or part geometry that do not translate neatly into a small clasp attached to a flexible, compressible strap.

In other words, there were ideas worth studying, but no ready-made answer. We were looking for a solution suited specifically to this category — a rubber strap system that needed to remain compact, intuitive, and robust.

Our design brief: what we wanted, and what we had to respect

By that point, our brief had become quite clear.

First, the mechanism had to be intuitive. If micro-adjustment was going to improve everyday wear, it had to feel simple enough that users would actually use it. It also had to work without an external tool. The whole point was to make small comfort adjustments easier, not to replace one inconvenience with another.

We also wanted the adjustment to be meaningfully finer than the permanent sizing already offered by the cut-to-size system. This was not about replacing the primary sizing method, but about complementing it with a smaller, quicker level of tuning.

At the same time, there were several constraints we were not willing to ignore. One of the most important was backwards compatibility. We wanted to remain inclusive towards existing owners of our CTS straps, which meant the new clasp should not require users to abandon the system they already owned. The mechanism also had to fit within the small physical envelope of the clasp itself. There was very little room to work with, and every fraction of a millimetre mattered.

And finally, it had to be robust enough for daily use while also reproducible at production scale. A mechanism that works well once in a prototype is only the beginning. For a launch product, it had to work reliably, repeatedly and consistently across batches and finishes.

The iterations

Iteration 1: A moving caddy inside the clasp

Our first concept tried to preserve the strap exactly as it was and solve the problem entirely within the clasp.

The idea was somewhat similar to how an adjustable car seat moves along a controlled track. The strap would sit in a caddy that could slide back and forth beneath the clasp head, allowing the effective length to change without affecting the strap itself. The caddy would lock into one of several positions through a trapped ball-bearing system, giving the user multiple points of adjustment while maintaining the same overall clasp style and size.

On paper, the concept was promising. It preserved compatibility with the existing strap architecture, kept adjustment on-the-fly and avoided the need to redesign the strap body.

But at this scale, conceptual viability and production viability turned out to be very different things. Once material behaviour, tolerances, part consistency and repeatable assembly entered the picture, the design became much harder to execute reliably. What seemed straightforward in principle proved difficult to reproduce with the consistency required of a finished product.

Still, the first iteration taught us something important: The problem could be solved within the clasp envelope, but only if the mechanism itself was simpler, more tolerant and better suited to real-world production.

Iteration 2: Adapting a proven idea

By this point, we were already working with the inventor of the Fitwell mechanism, which led us to a natural question: could a proven idea from an adjacent product category point the way forward?

Fitwell was compelling for several reasons. It already operated within similar constraints: a compact package, compatibility considerations and the need for convenient adjustment in daily use. Just as importantly, it was not merely theoretical. It was a mechanism with real-world precedent.

So we explored whether the same underlying principle could be integrated into our clasp system. From the beginning, this work was done in direct collaboration with the original inventor.

The early results were encouraging. The strap could still be installed in much the same way as before, while the spring bar could be captured in one of several positions within the clasp. Adjustment could then be made through a simple push or pull. The concept was elegant, mechanically efficient, and much closer to the user experience we had been aiming for.

But this was not yet the finished product. Even with a promising architecture in place, the demands of precision were high. The mechanism had to engage positively, resist accidental movement, actuate with the right amount of force, and do so consistently over repeated use. We also had to account for how material thickness, finishing processes, and production variation would affect that behaviour. Even different final finishes, such as black, yellow gold and rose gold, introduced variables that had to be carefully managed.

This second iteration gave us the right direction. The rest would come down to refinement.

Iteration 3: Turning a concept into a product

The final phase was less about changing the idea and more about perfecting it.

Fine-tuning became the real work. We refined dimensions throughout the mechanism, developed custom spring bar specifications with longevity in mind, and adjusted the positioning and geometry of the moving parts to balance actuation force, durability and reliability. Every detail had to serve more than one purpose: ease of use, structural confidence, repeatability and safety over time.

That process also meant thinking beyond whether the mechanism worked in a small number of successful tests. It had to remain dependable over many cycles. It had to resist failure. It had to behave consistently when made at scale. And it had to do all of this without leaving early adopters and later buyers with materially different experiences of the same product.

This was the point at which the product became real. Not because a single breakthrough suddenly solved everything, but because the mechanism had been refined enough to cross the distance between an interesting prototype and a product we could stand behind.

Function-testing for real-world use

A mechanism like this cannot simply work once. It has to work repeatedly, predictably and with the same feel over time.

To that end, we tested the mechanism by repeatedly actuating it — from the tighter position to the looser position, then returning it to the tighter position. We carried out 500 such cycles, totalling 1,000 individual movements of the mechanism.

This kind of testing mattered because the goal was not just motion, but controlled motion. The mechanism had to reliably release and capture the spring bar, maintain a consistent actuation feel and do so without drifting from the intended force profile.

Just as importantly, the target actuation force was not chosen in isolation. It was informed by testing across users of different demographics, accounting for variations in hand strength, dexterity and how people naturally interact with the clasp. The goal was to arrive at a force profile that felt secure enough to avoid accidental movement, while remaining intuitive and comfortable in daily wear.

During development, we also observed that under extreme or excessive use, the position of the deflecting arm could shift slightly, reducing the actuation force. To account for this, the mechanism can be re-adjusted manually, if required.

With the spring bar left in the tight position, firmly press the clasp mechanism against the edge of a hard surface protected by a soft cloth. This reseats the arm into its intended position and restores the intended actuation force.

What the final product represents

This clasp is the result of solving a very small problem that turned out not to be small at all.

What the user experiences is simple: A more practical way to fine-tune the fit of a rubber strap, quickly and intuitively, without tools. But behind that simplicity is a long chain of decisions about packaging, compatibility, force, durability, safety and production.

In that sense, the clasp represents more than just a new feature. It reflects a particular way of developing products: studying what already exists, understanding where those solutions stop short, respecting the constraints that matter, and then iterating until the mechanism feels as natural as it should have been all along.

The smallest interactions often take the most work to get right. This one was no different.