Strap for Hydroconquest Chronograph Tachymeter

The lug width of the Longines HydroConquest L3.651.4.16.6 is 21 millimetres. This measurement should always be verified using a digital calliper positioned between the two suspension bars, excluding the pins themselves. A 21mm strap is the only compatible option for this model; different widths (19mm, 20mm, 22mm) will not seat correctly.

The ideal strap depends on intended usage. For formal and daily wear, alligator leather in black or brown with natural tanning delivers elegance without compromising the watch's technical character. Shell cordovan with vegetable tanning develops a compelling patina over time. Vegetable-tanned calf offers concrete durability and longevity. For sport or diving applications, a NATO fabric strap or vulcanised rubber strap are the most functional choices.

Strap replacement is accomplished by extracting the suspension pins (the lateral case attachments). Position the watch on a soft surface, use an appropriate tool (a spring bar tool or small screwdriver) to gently push the pins outward, and extract completely. Insert the new 21mm strap by aligning the holes, reinsert the pins from outside to centre until you hear a click. Verify the strap is secure before wearing the watch.

Any high-quality strap with a 21mm lug width is compatible: alligator, vegetable-tanned calf, shell cordovan, nubuck, cotton NATO, synthetic silk, vulcanised rubber. Compatibility is determined solely by lug width, not by strap brand. Ateliers such as Casati Milano customise solutions respecting the watch's qualitative standards.

A quality leather strap, with routine maintenance, lasts 3–5 years under moderate daily use. Factors affecting durability include humidity exposure (accelerating ageing), washing frequency, body perspiration, quality of tanning, and leather thickness. Shell cordovan with vegetable tanning and vegetable-tanned calf typically last longer. A vulcanised rubber strap, with minimal care, offers superior longevity even in humid environments.