Strap for Master Collection 40mm Annual Calendar Stainless Steel / Black-Roman / Bracelet

The lug width of the Longines Master Collection L2.910.4.51.6 is 21mm. This measurement refers to the distance between the two anchor pins on the watch case where the strap is attached. To measure it accurately, place a ruler between the pin insertion points without including the pin diameter itself. On milanostraps.it, you will find all straps compatible with this 21mm lug width.

The best strap choice depends on your use case and aesthetic preference. For maximum formal elegance, we recommend a dark brown or black alligator strap; for warmth and vintage patina, vegetable-tanned calf with natural ageing is ideal; for versatility and sporting durability, shell cordovan is the perfect choice. On milanostraps.it, you can explore all these materials in 21mm, or contact Casati Milano atelier for a fully bespoke creation.

To change the strap, you will need a specific tool: a spring bar tool. Position yourself under good lighting, place the watch face-down on a soft cloth, and use the thin end of the spring bar tool to gently lift the horizontal pin until it disengages from the case seat. Repeat on the opposite side. Align the new strap's holes with the pin heads, which will lock automatically. This operation requires patience rather than force. If you prefer to avoid any risk, Casati Milano atelier offers professional installation.

Yes, absolutely. Aftermarket straps with a 21mm lug width are fully compatible with the L2.910.4.51.6, provided the pins are the same size (typically 1.5–1.8mm diameter, which is industry standard). Milanostraps.it supplies exclusively artisanal 21mm straps crafted to Longines technical specifications. Using a higher-quality aftermarket strap can actually improve the overall comfort and durability of your watch.

The durability of a leather strap depends on the material, frequency of use, and maintenance. A high-quality alligator strap, worn 5 days per week, typically lasts 5–7 years before requiring re-stitching. Vegetable-tanned calf, exposed daily to perspiration and humidity, has an average lifespan of 3–5 years; shell cordovan, being more resilient, can exceed 10 years. All artisanal straps from milanostraps.it include an 18-month warranty, and Casati Milano atelier offers restoration and maintenance services to significantly extend the useful life of your strap.