Strap for Spacematic Classic White

The lug width of the Fortis Cosmonaut 623.10.42 is 20 millimetres. This is the inner-to-inner distance between the watch case lugs. All compatible straps must have a total width of 20mm to fit correctly without adapters.

The ideal strap depends on your use case. For a rigorously avionic aesthetic, we recommend alligator or vegetable-tanned brown leather. If you prefer versatility, quality calf leather with evolving patina offers comfort and professional appearance. For sports and humid environments, FKM rubber provides grip and durability. NATO striped straps reference Swiss and civil aviation traditions.

Extract the spring bar connecting the strap to the case lugs using a dedicated tool (small screwdriver or strap removal tool). Insert the new 20mm strap into the lug, then reinsert the spring bar until it clicks into place. Verify the strap is firmly secured before wearing the watch.

Yes, all our straps in the 20mm collection are compatible with the Cosmonaut 623.10.42. We offer options in alligator, vegetable-tanned calf, shell cordovan, NATO and FKM rubber. Each strap is constructed with artisanal precision and can be personalised according to your colour preferences.

A quality natural leather strap with vegetable tanning has an average lifespan of 3-5 years with intensive daily wear. Longevity depends on climate, humidity and frequency of use. Leather straps evolve by developing a patina that increases their character. FKM rubber has a longer lifespan (5-7 years) in humid environments and water sports.