Tudor Black Bay 58 M7939A1A0NU-0001: A Closer Look at the METAS-Certified 39 mm Diver

The latest Tudor Black Bay 58 is a good example of how a watch can change substantially without abandoning the design that made it recognizable. Reference M7939A1A0NU-0001 keeps the familiar 39 mm format and black dive-watch appearance, but adds a revised case, a five-link bracelet with T-fit adjustment and the METAS-certified manufacture calibre MT5400-U.

That exact reference number matters. Tudor now offers several Black Bay 58 variations, including different dials, bezels, bracelets and GMT models. This article concerns only the black-dial, stainless-steel Black Bay 58 reference M7939A1A0NU-0001 on the five-link steel bracelet.

Image credit: Original editorial illustration created for RALLO Watches. Reference appearance checked against Tudor’s official product page for Black Bay 58 reference M7939A1A0NU-0001: https://www.tudorwatch.com/en/watches/black-bay-58/m7939a1a0nu-0001. Editorial illustration only; not an authentication reference.

What Tudor changed

At first glance, the watch still reads as a Black Bay 58: a compact steel diver with a black dial, a black bezel insert, gilt-toned details and Tudor’s snowflake hour hand. The changes become clearer when the specifications are examined.

Tudor lists the stainless-steel case at 39 mm in diameter and 11.7 mm thick, with a 20 mm lug width. The case combines polished and satin finishes. The crown has been redesigned to sit flush with the middle case, and the domed matte-black dial now uses applied hour markers. The dial text has also been reduced to two lines.

The bezel remains practical and traditional. It is a unidirectional rotating steel bezel with an anodized aluminum insert rather than ceramic. That choice gives the watch a softer, more vintage-minded appearance, but buyers should understand that aluminum can show marks and fading differently from ceramic over time.

The movement is the bigger story

Inside reference M7939A1A0NU-0001 is Tudor manufacture calibre MT5400-U, a self-winding mechanical movement with a bidirectional rotor and a 65-hour power reserve. Both COSC and METAS certify the movement and completed watch.

METAS Master Chronometer certification is more than a single timing test. Tudor states that the testing covers precision at two temperatures, in six positions and at two levels of power reserve. The completed watch is also tested for water resistance, power reserve and operation after exposure to a 15,000-gauss magnetic field. COSC certification is a prerequisite for the movement before the watch undergoes the METAS process.

For an owner, those laboratory standards translate into practical benefits. Magnetism from everyday electronics is a common cause of mechanical-watch timing problems. A watch tested to continue functioning accurately after 15,000-gauss exposure offers meaningful protection for normal modern use.

Built as an actual dive watch

The Black Bay 58 M7939A1A0NU-0001 is rated water-resistant to 200 metres, or 660 feet. It uses a screw-down crown, a domed sapphire crystal and a unidirectional bezel designed to measure elapsed dive time. A bezel that turns only counterclockwise is a safety feature: if it is moved accidentally, it can indicate less remaining time rather than more.

Water resistance should still be treated as a maintained capability rather than a lifetime promise. A pre-owned example should be pressure-tested before swimming or diving, especially if its service history is unknown or the crown, crystal or case has been opened.

Why the five-link bracelet matters

This reference is supplied on Tudor’s five-link stainless-steel bracelet with polished and satin finishes. The bracelet uses Tudor’s T-fit rapid-adjustment clasp, allowing the wearer to fine-tune the fit without a tool.

That is not a minor convenience. Wrist size changes during the day with temperature and activity, and a dive-style watch works best when it is secure without being tight. The five-link construction also gives this Black Bay 58 a more refined appearance than a conventional three-link tool-watch bracelet while preserving the steel sports-watch character.

What to verify before buying

Confirm the case or paperwork identifies reference M7939A1A0NU-0001 and confirm the matte-black domed dial, applied hour markers, black anodized-aluminum bezel insert and five-link steel bracelet with T-fit clasp described by Tudor for this reference.

Ask for clear photographs of the dial, bezel, case sides, lugs, case back, crown, bracelet and clasp. Keep the full serial number private in any public listing. Inspect the aluminum bezel insert for scratches, dents or fading, check crown action and clasp adjustment, ask about service history, and obtain a current water-resistance test before water use.

Treat boxes, cards and accessories as supporting documentation, not as proof that the watch itself is authentic or mechanically sound. An independent inspection remains worthwhile for any substantial pre-owned purchase.

The RALLO view

Reference M7939A1A0NU-0001 is not simply a cosmetic update to the Black Bay 58. The thinner 11.7 mm case, adjustable five-link bracelet and METAS-certified MT5400-U movement address three things owners feel every day: proportions, comfort and confidence in performance.

The watch still has a distinctly vintage-inspired face, but its engineering is current. That combination makes it especially appealing to someone who wants the character of an older dive watch without accepting vintage water resistance, fragile lume or uncertain movement condition.

The most important buying advice is also the simplest: use the complete reference number. Black Bay 58 now describes a family, not one watch. For the specific black-dial, five-link, METAS-certified steel model discussed here, the correct reference is M7939A1A0NU-0001.

Sources and fact check

Tudor official product page for Black Bay 58 M7939A1A0NU-0001: https://www.tudorwatch.com/en/watches/black-bay-58/m7939a1a0nu-0001. Specifications and certification details checked September 10, 2026.