Longines · HydroConquest

Strap for HydroConquest 39 Automatic Stainless Steel / Black / Bracelet

Takes 19 mm straps. Verified lug width, the straps that fit this model, and answers to the most common questions.

Lug width19 mm
Case diameter39 mm
ReferenceL3.780.4.56.6
FamilyHydroConquest
MovementLongines caliber L888.5 hours, minutes, seconds | date | chronometer
Year2022
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 L3.780.4.56.6

Selected for the 19 mm lug width

All 19 mm straps →

The HydroConquest L3.780.4.56.6, seen from the bench

The Longines HydroConquest L3.780.4.56.6 is a contemporary evolution of a diving line rooted in the 1960s. The stainless steel case with ceramic bezel and 39mm diameter offers 300 meters water resistance, combining robust construction with refined aesthetics. The L888.5 caliber movement, COSC-certified chronometer, provides ±4 seconds per day precision. Strap width is 19mm.

Frequently asked questions

What is the lug width of the Longines HydroConquest L3.780.4.56.6?

The lug width is 19mm, a specific measurement for this reference that does not correspond to standard industrial sizes such as 18mm or 20mm. Measuring the lug correctly is essential when purchasing compatible straps: position a digital calliper between the inner shoulders of both lugs, keeping the axis parallel to the case diameter. This measurement ensures harmonious proportions on the 39mm case.

What is the best strap for the Longines HydroConquest L3.780.4.56.6?

The choice depends on your intended use: for diving and aquatic activities, alligator in vegetable tanning or shell cordovan ensure moisture resistance and develop patina over time. For formal daily wear, Tuscan calf with stainless steel deployante offers elegant functionality. For intensive sports and diving, vulcanised rubber is unbeatable in durability and zero maintenance. Ideal colours include chocolate brown, deep black, or dark blue, which enhance the blue dial and ceramic bezel without competing visually.

How do I change the strap on a Longines HydroConquest?

The strap is attached to the case via two removable horizontal pins positioned between the lugs. Use a spring bar tool to gently press the pin and extract it from its seat. Once both ends of the old strap are free, slide the new strap under the lugs and reinsert the pins into their respective seats, using the tool to lever until they click into place. Verify that both pins are fully seated before wearing the watch.

Can I use a quality aftermarket strap on this Longines?

Absolutely. A bespoke 19mm strap crafted from premium leather with stainless steel deployante significantly elevates the tactile and aesthetic experience of the watch. The quality of the tanning, the finishing of the lug edges, the choice of thread all contribute to transforming the HydroConquest into a personal instrument. Casati Milano and specialised suppliers offer customisable options in size, colour and finish, ensuring precise compatibility.

How long does a leather strap last on a Longines HydroConquest?

Durability depends on the tanning method, use intensity and maintenance practices. An alligator or shell cordovan strap, both in vegetable tanning, lasts 3–5 years if exposed to frequent moisture (e.g. regular diving), up to 7–10 years if worn daily in a dry environment. Tuscan calf, more sensitive to moisture, has similar lifespan but requires periodic air-drying. Vulcanised rubber, lacking organic properties, lasts 5–8 years before losing elasticity. Proper care—swift drying after water contact, periodic conditioning with vegetable cream—substantially extends strap life.

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