Strap for HydroConquest 41 Automatic Stainless Steel / Matte Black / NATO

The lug width is 21 millimetres. This measurement is specific to the L3.781.4.05.2 model and is not interchangeable with 20mm or 22mm straps. To verify with precision, place your watch on a flat surface and measure the distance between the inner edges of both lugs: the result must be exactly 21mm. An incorrectly sized strap will create unwanted lateral play and compromise the attachment to the case.

For this model, we recommend alligator leather in vegetable tanning as the luxury choice: the natural grain and patina that develops over time create a fascinating contrast with the stainless steel case. Satin calf in vegetable tanning is the most versatile and practical alternative. For frequent aquatic use, shell cordovan offers superior moisture resistance. NATO straps in waxed canvas or nylon provide maximum practicality in sandy or humid environments.

The lugs of the Longines HydroConquest L3.781.4.05.2 are screw-down type to ensure water resistance. You will need a curved spring bar tool and a 1.5mm precision screwdriver. Gently unscrew the lug nut with anticlockwise movements until the pin releases. Remove the old strap and insert the new one by aligning the holes with the pin. Retighten with even pressure: the pin should be snug but not excessively tight to avoid damage to the threads.

Yes, aftermarket 21mm straps are completely compatible as long as they are manufactured to exact specifications (21mm lug width, appropriate thickness for the case). Mechanical compatibility is guaranteed: the important consideration is that the strap should not be significantly thicker than the original model, to avoid tension on the screw-down lugs. Milano Straps provides 21mm straps tested and guaranteed for this model.

A quality leather strap (alligator or calf in vegetable tanning) typically lasts 3–5 years with moderate daily wear. Durability depends on exposure to moisture, extreme temperatures and cleaning frequency. The Longines HydroConquest, being a true dive watch, undergoes greater stress in humid environments: if worn frequently in pools or at sea, we recommend limiting leather strap use to 2–3 years and alternating with NATO or rubber straps. Milano Straps' warranty covers 18 months against manufacturing defects.