Strap for Speedmaster Broad Arrow Co-Axial GMT Stainless Steel / Black

The lug width of the 3881.50.37 is 21mm. This dimension is critical to prevent lateral play of the strap: it must be measured internally between the spring bars, with no adjustment margin. Undersized straps will slip, oversized straps will create unwanted gaps.

Black or dark brown alligator offers formality and visual crispness; shell cordovan guarantees dramatic aging and vibrant texture; vegetable-tanned calf represents the compromise between lightweight structure and natural patina over time. The choice depends on use: professional suggests alligator, aesthetic suggests cordovan, daily suggests calf.

The 3881.50.37 uses standard spring bars. Position the watch on a soft surface, locate the spring bar holes (one on each side), push the spring with a thin tool or dedicated lever, remove the old lug and insert the new one by aligning the spring bars. Simple but delicate operation: avoid scratching the case.

Any strap with a 21mm lug width is compatible. Milanostraps.it offers a dedicated selection in alligator, shell cordovan, calf, fabric and rubber—all built to artisanal specifications for perfect tolerances on this critical measurement. The Casati Milano warranty covers durability and fit.

A quality leather strap, subject to regular use and minimal maintenance (occasional cleaning, protection from excessive moisture), lasts 4-7 years before showing structural failure. Shell cordovan, being harder, can exceed 10 years. The Casati Milano warranty is 18 months; after this period replacement depends on visible wear and leather flexibility.