Swatch · Sistem 51

Strap for Sistem Planet

Takes 20 mm straps. Verified lug width, the straps that fit this model, and answers to the most common questions.

Lug width20 mm
Case diameter42 mm
ReferenceSUTW404
FamilySistem 51
MovementSwatch caliber Sistem51 Date
CasePlastic

Spring bar

Swiss Standard universal spring bars

The right category for this model · 316L steel, all lug widths 13–26 mm

Straps for the Sistem 51 SUTW404

Selected for the 20 mm lug width · workshop selection

All 20 mm straps →

The Sistem 51 SUTW404, seen from the bench

The Sistem 51 was launched by Swatch in 2013 as the first automatic mechanical movement entirely assembled by machines. It features the Sistem51 caliber with 51 components, a power reserve of 90 hours, and a date indicator. The case has a welded monoblock construction, hermetically sealed and not serviceable.

Frequently asked questions

What is the lug width of the Swatch Sistem 51 SUTW404?

The SUTW404 features a fixed lug width of 20 millimetres. This is the orthogonal distance between the two spring bars that anchor the strap to the case. This specification is non-negotiable, so any aftermarket strap must be specifically manufactured for this width to ensure a secure fit without gaps.

Which strap material is most suitable for the Swatch Sistem 51 SUTW404?

The choice depends on usage and aesthetic preference. For a sartorial look, an alligator strap with vegetable tanning or vegetable-tanned calf leather is recommended, as it elevates the simplicity of the transparent case. For a sporty-casual aesthetic, a NATO strap in cotton or nylon is practical and economical. For humid or aquatic environments, a fluoroelastomer rubber strap offers durability without deterioration risk.

How do you change the strap on a Swatch Sistem 51 SUTW404?

Changing the strap requires a dedicated tool called a spring bar tool. Position the tool's tip under the spring bar from beneath the case, applying gentle upward pressure to release the current strap. Repeat with the second bar. Insert the new strap's spring bars into the lugs and click them firmly into place until fully secured. If uncertain, consult a professional to avoid damage to the plastic case.

Is any generic 20mm strap compatible with the SUTW404?

Yes, provided the strap explicitly bears a '20mm' marking or is SUTW-compatible. However, construction quality varies significantly: budget straps may exhibit gaps between case and band, undesired movement, or accidental unclasping. We recommend verified quality artisanal straps, where manufacturing tolerances are tighter and more reliable.

What is the typical lifespan of a leather strap on a Swatch Sistem 51?

A quality leather strap—alligator, vegetable-tanned calf—typically lasts 3 to 5 years with daily use and ordinary care. Longevity depends on exposure to moisture, perspiration, direct sunlight, and cleaning frequency. A strap subjected to frequent wetting without drying deteriorates faster. The patina that develops over time is normal and desirable; the strap should not be considered exhausted until it exhibits structural tears or separation.

The next step

The right strap isn't chosen. It is built, together.

From the atelier appointment to delivery, every step is made for those who know that things done well take time. Rare leathers, one piece at a time, eighteen months of warranty.

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Casati Milano · Via XX Settembre 15, Milan · by appointment only