Fortis · Cosmonaut

Strap for Spacematic Pilot Professional

Takes 20 mm straps. Verified lug width, the straps that fit this model, and answers to the most common questions.

Lug width20 mm
Case diameter40 mm
Reference623.10.71
FamilyCosmonaut
MovementETA caliber 2836-2 hours, minutes, seconds | date, day
CaseStainless 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 Cosmonaut 623.10.71

Selected for the 20 mm lug width · workshop selection

All 20 mm straps →

The Cosmonaut 623.10.71, seen from the bench

The Fortis Cosmonaut reference 623.10.71 features the automatic ETA 2836-2 caliber with hour, minute, second, date and day indications. The watch has 20mm lugs and derives from Fortis' tradition linked to Russian space missions. The ETA movement ensures reliability and easy maintenance.

Frequently asked questions

What is the lug width of the Fortis Cosmonaut 623.10.71?

The Fortis Cosmonaut 623.10.71 is fitted with 20-millimetre lugs. This dimension is standard for timepieces with a case diameter around 40mm and is compatible with the extensive range of artisanal straps available in this size. To verify compatibility with a specific strap, measure the distance between the spring bar pins on your case.

What is the best strap for the Fortis Cosmonaut 623.10.71?

The optimal strap choice depends on intended usage. To preserve the watch's original tool watch character, a polyamide NATO or FKM rubber strap is recommended. For daily versatility, alligator with vegetable tanning and refined grain offers elegance without stylistic compromise. For formal wear, a polished dark brown or black calf leather with a stainless steel deployant clasp is the most sophisticated choice.

How do I change the strap on my Fortis Cosmonaut 623.10.71?

Strap replacement involves removing the spring bar pins that secure the strap to the watch lugs. Use a spring bar remover tool or a small flat implement to gently compress the spring and slide the pin out of the lug. Insert the new strap onto the spring bars and reposition the pins. If uncertain, consult a professional watchmaker: the service takes less than 5 minutes.

Can I use a compatible aftermarket strap on my 623.10.71?

Absolutely. The 20mm lug width is a universal dimension, and any quality strap engineered for this size will be fully compatible with the Fortis Cosmonaut 623.10.71. The artisanal straps from milanostraps.it are constructed with precision craftsmanship and guarantee stable attachment and impeccable fit.

How long does a leather strap last on the Fortis Cosmonaut 623.10.71?

A quality leather strap, subjected to moderate use, typically lasts 3–5 years. Longevity depends on frequency of wear, exposure to moisture, and maintenance applied. An alligator with vegetable tanning ages elegantly and develops a fascinating patina over time. To extend durability, dry the strap after moisture exposure and periodically apply a specialist leather conditioner.

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