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Frederique Constant · Slim Line

Strap for Slimline Automatic Bracelet

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

Lug width

20mm
20 mm strapsAll Frederique Constant
Lug width20 mm
Case diameter40 mm
ReferenceFC-306S4S6B
FamilySlim Line
MovementFrederique Constant caliber FC-306 Hours, Minutes | Date
CaseStainless Steel

Spring bar

Swiss Standard universal spring bars

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

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Straps for the Slim Line FC-306S4S6B

Selected for the 20 mm lug width · workshop selection

All 20 mm straps →

The Slim Line FC-306S4S6B, seen from the bench

The Frederique Constant Slim Line FC-306S4S6B is a 40mm stainless steel automatic watch with manual winding, powered by the FC-306 caliber offering a 42-hour power reserve. It features hours, minutes, and date window on the dial. The watch has a 20mm lug width, characteristic of the Slim Line collection, which emphasizes balanced proportions and functional minimalism. Founded in Geneva in 1988, Frederique Constant designed this model to be understated and adaptable to both formal and everyday contexts.

Frequently asked questions

What is the lug width of the Frederique Constant Slim Line FC-306S4S6B?

The Frederique Constant Slim Line FC-306S4S6B features a lug width of 20mm. This dimension is proportioned to the 40mm case diameter and is the standard size for all straps compatible with this model. To verify your lug width, measure the internal distance between the two metal lugs on the case—it should measure exactly 20mm.

What is the best strap for the Frederique Constant Slim Line?

The best strap depends on your intended use. For formal occasions, black or dark brown alligator emphasizes the minimalist elegance of the model. A calf leather with vegetable tanning in brown is ideal if you appreciate the natural patina that develops over time. For technical versatility, an FKM rubber strap offers durability and water resistance without aesthetic compromise. A grey-blue NATO strap is perfect for casual contexts.

How do I change the strap on my FC-306S4S6B?

The process is straightforward: locate the two metal lug pins that secure the strap to the case lugs. Using a spring bar tool or small flat implement, gently push the pin outward to free the strap. Align the new strap's holes with the lugs and reinsert the pin. Verify that the strap is perfectly centered and that the upper lugs are securely fastened. Do not apply excessive force to avoid damaging the case shoulders.

Can I use an aftermarket strap compatible with the FC-306S4S6B?

Yes, absolutely. All straps with a 20mm lug width are compatible with the FC-306S4S6B. Milano Straps offers an extensive range of artisanal straps in alligator, calf, shell cordovan, and technical materials, all customizable in width, colour, and construction specifications. A high-quality aftermarket strap can completely transform the aesthetic character of your watch.

How long does a leather strap typically last on a Frederique Constant watch?

The lifespan depends on the material and frequency of use. A calf leather strap with vegetable tanning, with proper care, lasts 3-5 years of daily wear. Alligator, being a denser and more structured leather, can last 5-7 years. Shell cordovan, thanks to its semi-structured nature, extends durability to 8 years. An FKM rubber strap has nearly unlimited lifespan (10+ years), provided it is protected from prolonged direct UV exposure. Milano Straps offers an 18-month guarantee on all artisanal straps produced.

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