Strap for HydroConquest 39 Automatic Stainless Steel / Black / Rubber

The lug width of the Longines HydroConquest L3.780.4.56.9 is 19 millimetres. This measurement refers to the distance between the pins that attach the strap to the watch lugs. To verify this precisely, insert a calliper horizontally between the two lugs: it should read exactly 19mm. A compatible strap must have an identical width to ensure perfect fit without lateral play or misalignment.

The ideal strap depends on intended use and aesthetic preference. For formal and mixed diving environments, we recommend black or dark brown alligator with vegetable tanning, offering both elegance and robustness. For maximum versatility, calf leather with subtle grain provides the best compromise between aesthetics and durability. If water sports predominate, vulcanised rubber or grey canvas NATO fabric will preserve the strap integrity during repeated immersions whilst maintaining a professional, understated appearance.

To change the strap, obtain a soft brush (to protect the case), a small flat-head screwdriver, and your new 19mm strap. Place the watch on a soft surface, gently lever the screwdriver under one of the pins (the metal rings passing through the lugs), and extract the pin by applying steady pressure. Repeat on the other side. Once the old strap is removed, insert the pins into the new strap, aligning them perfectly with the lugs, and push until they click into place. After fitting, verify that the strap sits flush with no lateral movement.

Yes, any strap with 19mm lug width is compatible with the Longines HydroConquest L3.780.4.56.9. At milanostraps.it you will find a curated selection of artisanal straps in leather, rubber, and canvas, customisable in length, initials, and thread colour. The Casati Milano atelier also offers made-to-measure straps with direct leather selection and styling consultation, backed by an 18-month workmanship guarantee.

A high-quality natural leather strap, crafted from vegetable-tanned leather such as shell cordovan or calf, can last 3–5 years of daily wear with regular maintenance. Longevity depends on humidity exposure (your Longines is water-resistant to 300m, but the strap requires air-drying after water contact), frequency of wear, and storage conditions. Robust leathers such as alligator tend to last slightly longer. To extend lifespan, always dry the strap after water contact and apply a light mink oil treatment every 6–8 months.