Strap for Speedmaster Perpetual Calendar Yellow Gold / Champagne /

The lug width of the 3650.10.20 is 18 millimetres. This width is a standard construction specification for the model: the lateral lugs of the case require a strap with an internal passant of exactly 18mm, with no adjustment margin. The precision tolerance is ±0.2mm. Any attempt to force a 20mm or 16mm strap would damage both the strap and the watch lugs.

For yellow gold, vegetable-tanned alligator is the most natural choice: its regular grain and the patina that develops over time create an authentic aesthetic dialogue with the precious metal. Alternatively, shell cordovan in burgundy or cognac offers luxury without formal rhetoric. Polished black calf introduces severe contrast, ideal for those who appreciate the sporty register of the chronograph. For contemporary use, a dark grey NATO with natural linen stitching reinterprets the model toward practicality and resilience. The choice depends on the balance desired between formality and functionality.

Position the watch on a flat, horizontal surface. Use a precision calliper and measure the distance between the inner edges of the two lateral lugs. This measurement must be exact: 18 millimetres for the 3650.10.20. Do not measure from outer edge to outer edge. Keep the calliper perpendicular to the watch plane, without applying pressure. If you do not have a calliper, contact Casati Milano: the team verifies the measurement via photograph with scale indication and guarantees compatibility before creation.

Yes, any certified 18mm strap is compatible with the 3650.10.20, but construction quality varies significantly. A generic 18mm strap purchased online may present imprecise construction tolerances (internal passant of 18.3mm instead of exactly 18mm), causing lateral play and accelerated wear on the lugs. Casati Milano's artisanal straps are made with custom-cut lugs and individually calibrated passants to guarantee perfect fit. For significant investments like the 3650.10.20, bespoke represents the conscious choice for durability and aesthetic reliability.

An alligator strap with vegetable tanning, used daily on a 3650.10.20, maintains structural integrity and elasticity for 8–12 months of constant use. After this period, the leather begins to develop microscopic cracks in the grain, especially in the passant flexure zones. Box calf lasts slightly less (6–10 months), while cordovan, due to its superior protein density, can extend life to 18 months. Factors such as humidity, frequency of use, and maintenance (conditioning with cream) directly influence longevity. Casati Milano offers an 18-month warranty and allows replacement of worn straps at reduced price for loyal customers, thereby supporting the sustainability of the watch's life cycle.