Fortis
Cosmonaut 623.10.52— lug 20mm

The Fortis Cosmonaut 623.10.52 features a lug width of 20mm, meaning the internal distance between the two strap lugs is exactly 20 millimetres. This measurement allows you to fit a broad range of aftermarket straps, whether in leather, fabric, or rubber.

The optimal strap choice depends on your intended use: for an elegant aesthetic, vegetable-tanned alligator in cognac or brown highlights the subtle satinised steel case. For sportier styling, a cotton NATO or natural rubber strap maintains the functional austerity of the watch. A full-grain calf leather offers a pragmatic balance between elegance and everyday practicality.

The straps on the 623.10.52 are changed by removing the spring bars that connect the strap to the case lugs. You will need a dedicated spring bar tool to gently press the lateral bars and free the old strap. The new 20mm strap is installed by aligning its holes with the bars, allowing them to close securely. If you are uncertain, a professional watchmaker can complete the task in minutes.

Any strap with a 20mm lug width is compatible. This measurement is standard across many sports and military watches. Milanostraps supplies a range of artisanal straps for 20mm lugs, in alligator leather, calf, shell cordovan, NATO, and rubber—each constructed with authentic quality and artisan finishing techniques.

A high-quality leather strap, worn daily, typically lasts 3 to 5 years. Vegetable-tanned leather ages more gracefully than industrial methods, developing a distinctive patina. Prolonged water exposure reduces leather longevity; many Cosmonaut owners therefore rotate their leather straps with rubber or NATO options during summer or sports-oriented periods.