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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-306S4S6B2
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-306S4S6B2

Selected for the 20 mm lug width · workshop selection

All 20 mm straps →

The Slim Line FC-306S4S6B2, seen from the bench

The Frederique Constant Slim Line FC-306S4S6B2 is a 40mm stainless steel watch powered by the manually-wound FC-306 caliber operating at 3 Hz. The satin-finished steel case houses a slightly domed dial available in deep blue or milky white, fitted with applied indices and a date window at 3 o'clock. The integrated steel bracelet with tapered links maintains visual continuity with the case. Water resistance is 30 meters, suitable for daily wear. The 20mm lug width is precisely dimensioned to complement the 40mm case proportions and accommodate aftermarket straps.

Frequently asked questions

What is the exact lug width of the Frederique Constant Slim Line FC-306S4S6B2?

The lug width of the Frederique Constant Slim Line FC-306S4S6B2 is 20 millimetres. This dimension represents the internal distance between the case lugs and is essential for selecting the correct aftermarket strap. Any strap intended for this model must be exactly 20mm wide to ensure precise fitting and correct visual proportions.

Which strap is most suitable for the Frederique Constant Slim Line FC-306S4S6B2?

For the Slim Line, alligator leather with vegetable tanning in brown or cognac represents the pinnacle choice, as it emphasises the case's minimalist elegance. Full-grain calf leather with vegetable tanning offers softness and authentic patina development over time. For more versatile daily use, cotton nato fabric ensures durability. Your choice depends on usage context and dial colour: with blue, favour brown or cognac; with white, black or taupe grey are ideal.

How do you change the strap on a Frederique Constant Slim Line FC-306S4S6B2?

Strap replacement is accomplished by unscrewing the spring bars that connect the strap to the case lugs. Use a dedicated spring bar tool to release the bars and slide the strap out of the lugs. Insert the new strap by aligning the loops with the bars, then secure firmly. It is advisable to entrust this operation to an expert if unfamiliar with the procedure, thereby avoiding scratches or damage to the lugs.

Are there quality aftermarket straps compatible with this model?

Yes, Milano Straps offers a wide selection of 20mm straps crafted in alligator, calf leather with vegetable tanning, cotton nato and rubber. All are compatible with the FC-306S4S6B2 and customisable in length, initials and stitching thread colour. The Casati Milano atelier additionally provides bespoke strap creation services with personal leather selection, 18-month warranty and WhatsApp support throughout the process.

How long does a leather strap last on a Frederique Constant Slim Line FC-306S4S6B2?

A quality leather strap, crafted in alligator or calf leather with vegetable tanning, lasts approximately 3–5 years with regular daily use, developing increasingly rich patina over time. Longevity depends on frequency of wear, climatic conditions (humidity accelerates ageing) and care practices. Protecting the strap from prolonged sun exposure and excessive moisture significantly extends its lifespan. nato and rubber straps offer greater durability due to their structural robustness.

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