Strap for Master Collection 40 Moonphase Stainless Steel / Black-Diamond / Bracelet

The lug width (ansa) of the Longines Master Collection L2.909.4.57.6 is 21.00mm. This measurement represents the distance between the two suspension pins of the case where the strap attaches. To verify compatibility with a new strap, use a digital calliper positioned perpendicularly between the internal shoulders of the two pins: the value must be exactly 21.00mm, with a tolerance of ±0.1mm.

The best strap depends on your intended use. For formal and executive settings, we recommend American alligator (Alligator mississippiensis) at 1.2–1.4mm thickness, which offers effortless elegance and a natural geometric pattern. For versatility and chromatic development over time, European grained calf leather with vegetable tanning is ideal: the leather progressively evolves towards richer, darker tones. For dynamic use, premium FKM rubber guarantees water resistance and thermal stability. The recommended colour pairing for the Master Collection's grey-blue dial is dark brown, burgundy, or black with coordinated stitching.

Strap replacement requires extracting the two spring bars (small horizontal springs inserted into the case pins). Proceed as follows: position the watch on a soft surface with the caseback facing up. Use a spring bar tool (a specialized tool with two flat tips) to push downward on one of the springs whilst simultaneously removing the pin from the case shoulder. Repeat for the other side. Insert the new strap by aligning the holes with the shoulders, then reinsert both pins using the spring bar tool. Verify that the pins are fully inserted and that the strap is perfectly symmetrical relative to the case.

Yes, any aftermarket strap (non-Longines) with a 21mm lug width is compatible with the Master Collection L2.909.4.57.6, provided that the strap's holes correspond exactly to the pin width (21.00mm ±0.1mm). High-quality bespoke leather straps additionally allow you to select material (alligator, calf, rubber), colour, thickness, and stitching type, delivering a superior aesthetic and tactile result compared to standard straps. Before purchase, always verify the compatibility dimensions provided by the manufacturer.

Leather strap longevity depends on material, tanning process, and usage frequency. High-quality alligator with vegetable tanning typically lasts 3–5 years with daily wear, developing a progressive patina that increases its aesthetic value. European grained calf leather has similar durability, 3–5 years, with the characteristic of darkening and enriching tonally over time. If worn occasionally (2–3 times per week), lifespan extends to 6–8 years. Premium FKM rubber is more durable (7–10 years) as it resists oxidative damage. Constant humidity and prolonged sun exposure accelerate ageing: store the strap in a dry environment away from direct light when unworn. An 18-month warranty is standard for bespoke straps from specialised ateliers.