Strap for Seamaster 300 Master Co-Axial Stainless Steel / Sedna Gold / Black / Bracelet

The lug width is 21mm. This width is characteristic of the two-tone Sedna Gold and stainless steel version and is present on both sides of the case (between one lug and the other). You can verify it with a digital caliper by positioning it at the two attachment points of the strap on the case.

For a Seamaster 300 in Sedna Gold and stainless steel, we recommend an authentic alligator in chocolate brown or cognac, or a shell cordovan for those seeking rarity and natural patina. These materials respect the warmth of the Sedna and age elegantly. Alternatively, quality calf leather with vegetable tanning offers immediate softness and smooth texture. Avoid compensations that are too dark, as they flatten the two-tone aesthetic.

The Seamaster 300 uses standard 21mm spring bars. With the watch face down, insert a spring bar tool or small flat screwdriver under the strap terminal, applying calibrated pressure to push the internal metal pin downward. Once released, the strap slides away. For installation, align the holes of the new strap with the case pins and use the tool to compress and insert the pin until you hear a click.

Yes, an aftermarket strap with 21mm lug width is perfectly compatible. The inner shoulder must fit correctly around the case (verify the precise case width between the two pins), but any reputable manufacturer already sizes straps according to standard. We recommend measuring the terminal thickness to avoid friction with the lugs, especially with rigid straps like shell cordovan.

A quality leather strap (alligator, cordovan, calf with vegetable tanning) typically lasts 3-5 years of daily wear, with variables related to sweat, humidity, and frequency of sun exposure. Shell cordovan tends to last longer thanks to its fibrous density. The patina that develops is not wear, but acquired beauty. Casati Milano offers an 18-month warranty on artisanal straps and recommends periodic maintenance to extend their useful life.