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Omega · X-33 / Z-33

Strap for Speedmaster X-33 Titanium / Red Kevlar / 2nd Gen

Takes 20 mm straps. Verified lug width, the straps that fit this model, and answers to the most common questions.

Lug width

20mm
20 mm strapsAll Omega
Lug width20 mm
Case diameter42 mm
Reference3991.50.41 (aka: 39915041)
FamilyX-33 / Z-33
MovementOmega caliber 1666 Hours, Minutes, Small Seconds, Additional 24 Hour Hand (adjustable) | Date, Month, Perpetual Calendar, Year Indicator | Chronograph, Countdown, Flyback, Foudroyante, Rattrapante | Alarm
CaseTitanium

Recommended spring bar

Spring bars Omega 20mm — 1.8mm diameter

Technical match for lug width and diameter · lug 20 mm · Ø 1.8 mm

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Straps for the X-33 / Z-33 3991.50.41 (aka: 39915041)

Selected for the 20 mm lug width · workshop selection

All 20 mm straps →

The X-33 / Z-33 3991.50.41 (aka: 39915041), seen from the bench

The Omega Speedmaster X-33 Titanium model 3991.50.41 is a specialized chronograph developed for European Space Agency and NASA astronauts and military pilots. It features a 42 mm titanium Grade 5 case, a thermocompensated quartz movement (Omega caliber 1666) at 5 Hz with perpetual calendar, flyback chronograph, rattrapante function, foudroyante display, and alarm. The 20 mm lug width accommodates the included Red Kevlar strap. Designed for extreme environments rather than luxury aesthetics, this instrument offers radiation resistance, corrosion protection, and precision of ±15 seconds per month across temperatures from -10°C to +60°C.

Frequently asked questions

What is the lug width of the Omega X-33 / Z-33 3991.50.41?

The Omega X-33 / Z-33 3991.50.41 features a <a href="/pages/termine-glossario/misura-ansa">lug width</a> of 20mm, which is non-standard in the retail market. This width is specific to Omega's aviator models and requires dedicated straps. Measuring lug width means calculating the distance between the spring bars that anchor the strap to the case: position a ruler on the inner diameter of the lug and read the value in millimeters.

What is the best strap for the Omega X-33 / Z-33 3991.50.41?

For this professional instrument we recommend three options: dark brown <a href="/pages/termine-glossario/alligatore">alligator</a> with <a href="/pages/termine-glossario/concia-vegetale">vegetable tanning</a> for understated elegance; dark grey nubuck calf for modern contrast with the titanium; black or grey ballistic NATO for tactical functionality. The choice depends on use: formal, everyday or technical.

How do I change the strap on my Omega X-33 / Z-33 3991.50.41?

Position the watch with the lug facing toward you. Locate the upper and lower spring bar: use a dedicated tool (spring bar tool) to compress the mechanism inward, releasing the used strap. Repeat on the other side. To mount the new strap, align the spring bars with the lug grooves (remember the orientation of the clasps!) and press until you hear a click.

Which aftermarket straps are compatible with the 3991.50.41?

Any strap with a <a href="/pages/termine-glossario/misura-ansa">lug width</a> of 20mm is compatible. Milanostraps offers a <a href="https://milanostraps.it/collections/cinturini-orologi-per-misura-ansa-20mm">collection dedicated to 20mm</a> in premium leathers, with customization options (initials, thread color, custom length). Our craftsmen manually verify compatibility with original Omega spring bars.

How long does a leather strap last on a professional watch like the X-33 / Z-33?

A quality leather strap (alligator, calf, shell cordovan) typically lasts 4-5 years with daily use, longer with proper maintenance (quarterly conditioning, protection from water and sweat). Durability depends on the tanning: vegetable-tanned leathers age with a characteristic patina, while chrome-tanned ones wear more quickly. For professional instruments like the 3991.50.41, we recommend having two straps and alternating them.

The next step

The right strap isn't chosen. It is built, together.

From the atelier appointment to delivery, every step is made for those who know that things done well take time. Rare leathers, one piece at a time, eighteen months of warranty.

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Casati Milano · Via XX Settembre 15, Milan · by appointment only