Zenith
El Primero 03.2153.400/78.C813— lug 21mm

The lug width of the Zenith El Primero 03.2153.400/78.C813 is 21 millimetres. This measurement is specific to this model and requires careful measurement to avoid errors. Use a digital calliper, positioning it between the lugs of the case and measuring from the centre of one seat to the other. A tolerance of ±0.2 millimetres is generally acceptable, however Casati Milano calibrates all handcrafted straps with deviations below 0.1 millimetres.

For this 42-millimetre chronograph in stainless steel, the most recommended materials are: natural alligator for sophisticated contrast with evolving patina over time; calf leather treated with vegetable tanning in dark brown or deep blue for balance between sportiness and luxury; NATO in ballistic canvas for explicit sporting vocation; vulcanised rubber for thermal comfort in warm climates. The choice depends on primary use and personal aesthetic preferences.

To change the strap, position the watch on a soft surface and use a spring bar tool to compress the internal springs of the lugs. Insert the lever into one of the lateral holes of the seat and gently lift the lug, disengaging it from the case. Repeat the operation on the opposite side. For installing the new strap, align the holes with the lugs and press until fully inserted, verifying that the lug is locked in both seats.

Yes, it is possible to use compatible aftermarket straps provided they respect the 21-millimetre lug width. High-quality straps made by specialist artisans such as Casati Milano offer the same durability and comfort standards as original straps, maintaining the wearing geometry without compromise. It is essential to verify the manufacturing tolerance (±0.2 mm) to avoid axial play.

The lifespan of a leather strap depends on the material, frequency of use, and environmental conditions. A calf strap with vegetable tanning can last 3–5 years with regular use, gradually developing patina and shifting in tone. Natural alligator tends to last longer (5–7 years) thanks to the denser structure of the leather. Vulcanised rubber offers superior longevity (7–10 years) in humid or warm environments. Casati Milano guarantees 18 months on all handcrafted straps, covering manufacturing defects.