Longines · HydroConquest

Strap for HydroConquest 41 Automatic Stainless Steel - Yellow Gold / Black / Rubber

Takes 21 mm straps. Verified lug width, the straps that fit this model, and answers to the most common questions.

Lug width21 mm
Case diameter41 mm
ReferenceL3.781.3.56.9
FamilyHydroConquest
MovementLongines caliber L888.5 hours, minutes, seconds | date | chronometer
Year2021
CaseCeramic, Stainless Steel

Spring bar

Swiss Standard universal spring bars

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

Straps for the HydroConquest L3.781.3.56.9

Selected for the 21 mm lug width · workshop selection

All 21 mm straps →

The HydroConquest L3.781.3.56.9, seen from the bench

The Longines HydroConquest L3.781.3.56.9 is a 41 mm stainless steel automatic diving watch featuring the L888.5 caliber with silicon hairspring, 33 jewels, and 64-hour power reserve. The unidirectional ceramic bezel in dark grey and 300-meter water resistance reflect decades of underwater instrument design. The 21 mm lug width accommodates the case-to-wrist proportions typical of this professional diving watch category.

Frequently asked questions

What is the lug width of the Longines HydroConquest L3.781.3.56.9?

The lug width of the Longines HydroConquest L3.781.3.56.9 is 21 millimetres. This measurement represents the distance between the two metal pins that connect the strap to the watch case. It is essential to verify this dimension before purchasing a replacement strap, as an incorrectly sized lug will not fit the case properly and compromises both the aesthetics and secure wear.

Which strap is most suitable for the Longines HydroConquest L3.781.3.56.9?

The most suitable strap depends on your intended usage. For daily wear and occasional diving, we recommend vegetable-tanned leather or shell cordovan, which develop a natural patina over time. For regular diving in saltwater environments, a vulcanised rubber strap offers the greatest durability and practicality. Alligator remains the premier aesthetic choice for those who do not engage in frequent submersions. Consult our specialists at atelier Casati Milano for personalised guidance based on your specific requirements.

How do you change the strap on the Longines HydroConquest L3.781.3.56.9?

Strap replacement is accomplished by extracting the lateral pins that connect the strap to the case lugs. Using a spring bar tool (typically a small dual-ended extractor with flat tips), insert the ends into the lateral slots of the pins and apply gentle pressure to release them. Remove the strap, clean the pins of any residue, and insert the new strap using the same method. If you lack experience, consult a professional watchmaker to avoid inadvertent scratching of the case. Our artisanal straps include detailed instructions.

Which aftermarket straps are compatible with the Longines HydroConquest L3.781.3.56.9?

Any strap with a 21 mm lug width is compatible with the Longines HydroConquest L3.781.3.56.9. Our catalogue features straps in alligator, vegetable-tanned leather, shell cordovan, rubber, and technical fabric, all available in the 21 mm size. All our straps are customisable in length, initials, and thread colour. Artisanal-quality straps offer superior tactile experience and longevity compared to standard industrial alternatives.

What is the lifespan of a leather strap for the Longines HydroConquest L3.781.3.56.9?

The lifespan of a leather strap depends on material, tanning process, and intensity of use. A quality vegetable-tanned calf leather, with proper maintenance (avoiding prolonged direct sunlight and unrinsed saltwater exposure), can last 3–5 years. Shell cordovan, owing to its microscopic density, can exceed 8–10 years. Well-maintained alligator leather typically lasts 4–6 years. Vulcanised rubber, conversely, has a practical lifespan of 2–3 years before showing signs of elasticity degradation. Casati Milano offers an 18-month warranty on all straps and provides restoration and repair services.

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