Strap for Seamaster Aqua Terra 150M Co-Axial 38.5 Stainless Steel / Grey

The Omega Aqua Terra 231.13.39.21.06.001 has an exact lug width of 18mm. This dimension is fundamental when purchasing any aftermarket strap compatible with this model. Precise measurement is performed by positioning a digital caliper from the inside of the upper lug to the lower one, at the narrowest insertion point. 17.5mm straps will be too tight and prone to slipping; 18.5mm straps will present insertion difficulties.

The ideal strap depends on intended use. For aesthetic coherence with the teak dial, we recommend a matte black alligator or dark brown shell cordovan that develops patina over time. For daily use in mixed environments, vegetable-tanned calf leather ensures chromatic stability and durability. For occasional water activities or sports, Swiss dark grey rubber offers high friction coefficient while maintaining visual sobriety. The 18mm straps from Milano Straps cover all these categories with precise tolerances.

Strap replacement requires a spring-bar tool or dedicated remover. Insert the tip of the tool into the lateral hole of the lug, compressing the internal pin toward the opposite side. Once under tension, the pin slides laterally and extracts. Position the new strap by aligning the hole at its end to the pin, then reinsert the pin into the opposite hole and release the tool tension. This operation requires precision: minimal risk of scratching if executed with correct tools (never use screwdrivers, which damage the case).

Yes, provided they respect exactly the 18mm lug width. Compatibility is not guaranteed by approximate widths (17.8mm, 18.2mm) but rather by tolerances of ±0.1mm. An 18mm strap crafted with metrological care—such as those from Milano Straps—inserts into the original Omega pin without lateral play and without stress on case materials. Low-quality generic straps, even if labeled 18mm, frequently present construction deviations that compromise fit.

A quality leather strap (alligator, shell cordovan, vegetable-tanned calf) on a wrist regularly exposed to sunlight and movement has an average lifespan of 4–6 years. Alligator tends to last longer thanks to robust cranial structure; shell cordovan is more fragile to concentrated mechanical stress but develops appreciable patina. Vegetable-tanned calf offers the optimal compromise of durability-aesthetics. Wear is not pathology, but natural evolution: A worn strap can be restored by specialized ateliers such as Casati Milano or replaced. Milano Straps' 18-month warranty covers construction defects, not temporal wear.