Sinn U1

Submarine steel and a hardened bezel

Sinn introduced the U1 in 2005 as a 1,000 m automatic dive watch. A catalogue from Sinn's 2009 and 2010 range lists the standard U1 at 44 mm in diameter and 14.3 mm thick, with a 22 mm lug width, sapphire crystal, solid caseback and a rating of 100 bar, which is 1,000 m. Those are the figures a specialist will check against the watch when it arrives.

The bezel is the notable feature. Sinn's catalogue identifies it as treated with TEGIMENT, which the brand describes as a surface hardening rather than a coating. The hardening makes the surface scratch-resistant but not scratch-proof. Sinn does not publish the process temperatures or depths, so any shop's description of the treatment should be treated as general.

The case is described as German submarine steel, but that does not mean every part of it is TEGIMENT-hardened. The catalogue ties the treatment to the bezel. Keep that distinction clear when you describe the watch to a shop or a buyer, because it changes how a scratch or chip should be handled.

Movement generations and what they mean for service

The circa-2010 U1 used the ETA 2824-2 automatic. Later U1 specifications list the Sellita SW 200-1, and Sinn's November 2025 specification sheet also lists the Sellita. A movement is a generation marker, so check the caliber on the watch before you order parts or agree to a service.

Both calibers are well understood by experienced watchmakers, so the movement itself is rarely the hard part. The real work is in the seals. A specialist should plan a pressure test at the start and at the finish, check the crown and caseback seals, and replace the gaskets that the depth rating depends on, using parts the shop can document.

Sinn's service centre is in Frankfurt, and its service information gives a timeframe of four to eighteen weeks. An independent can handle the movement and seals, but ask whether they can get genuine seals and bezel parts for your reference, and whether they are comfortable working on TEGIMENT surfaces. A shop that will not say what it can and cannot do with the bezel is one to avoid.

Checking a pre-owned U1

Start with the caliber and the bezel. A U1 with an ETA movement and one with a Sellita are different production generations, so confirm the caliber against the caseback or a photo. Look closely at the bezel edge for wear and chips, and do not accept a general description of the bezel's condition.

Test the bezel. Turn it, check the click and the alignment with the minute track, and look at the edges for chips. Sinn's service price list says TEGIMENT case components and bracelets cannot be reconditioned by polishing, so serious damage generally means replacement rather than restoration.

Ask for the service record and any pressure test certificate. A U1 that has been opened by a shop without the right tools may show marked screws or a loose caseback. A written inspection before purchase is more useful than a photograph of the dial, because it covers the seals, the movement and the bezel together.

Care and originality

Rinse the U1 in fresh water after seawater, and have the seals checked at each service. Sinn's care guidance calls for a water-resistance check at least once a year. A 1,000 m rating means little if the gaskets have aged, so the pressure test is what shows the watch is still sealed.

Straps age quickly in salt and sun. Replace them when they crack or harden, and keep a spare for regular use in the sea. Bracelets and case components with TEGIMENT cannot be polished back to condition, so a scratch that matters is a replacement question.

Originality is about the dial, hands and bezel insert. A replaced insert or a refinished bezel changes the watch, so ask for those changes in writing. Keep the box and papers with the watch, because they confirm the reference and the production period.

Owning a 1,000 m diver

A U1 is a tool watch, so think about where it will be used. Frequent saltwater use, sand and sun all work against the strap and the case edges. Rinsing after the sea, drying the strap and checking the crown after each trip cut down on the work that comes back to the shop.

When you book a service, ask the shop to record the seal and bezel condition before any work starts, with photographs if it can provide them. That record protects you if a later shop disagrees about what was there when the watch arrived. A 1,000 m rating is only as good as the most recent pressure test.

Treat the bezel as a working part of the watch. Turn it after each dive or swim to check the action, and rinse grit out of the edges. A bezel that begins to feel gritty or uneven is worth having checked before the next time the watch goes in salt water, since the bezel is often checked alongside the seals at service.

What to check on a Sinn U1

• Experience with TEGIMENT surfaces and a plan for chips and deep marks
• A pressure test before and after the work, with a written certificate
• Clear identification of the U1's caliber generation, ETA or Sellita
• Genuine seals and bezel parts, or a clear route to get them

Common questions