Both watches share the same Sinn formula: sapphire crystal front and back, 20 bar water resistance, low-pressure resistance, antimagnetic protection to DIN 8309, a screw-down crown and a Sellita-based automatic movement.
What separates them is 2.5 mm of diameter, a day complication, a bidirectional pilot's bezel — and two different ideas of what an everyday watch should look like.
Sinn · ~$1,650556 I
Sinn · ~$1,600104 St Sa IThe 104 is not simply a bigger 556. Its captive pilot's bezel with minute ratcheting and luminous key mark, day-of-week display and polished case make it the more complete instrument watch — and the one that reads as unmistakably Sinn to anyone who knows the brand's cockpit-clock heritage.
The 556 I measures 38.5 mm across, roughly 11 mm thick and about 65 g without a strap. The 104 St Sa I measures 41 mm, about 11.9 mm thick and roughly 73 g. Both share a 20 mm lug width, so strap ecosystems are interchangeable. The 556 disappears on the wrist and suits wrists under roughly 17 cm; the 104 has noticeably more presence and suits larger wrists, or buyers who want a watch that reads at a glance across a desk.
The 556 runs a Sellita SW200-1 with date only and a fixed bezel. The 104 runs a Sellita SW220-1 with day and date, plus a captive, bidirectional pilot's bezel with minute ratcheting and a luminous key mark at 12. Both beat at 28,800 vph with hacking seconds and antimagnetic protection to DIN 8309. The 104 answers three questions at a glance — time, day, date — and its bezel handles elapsed-time or countdown tasks the 556 cannot; the bezel is a timing tool, not a diving instrument — both are 20 bar watches, not dive watches.
The 556's satinized case, fixed bezel and sparse baton dial sit as comfortably under a shirt cuff as on a NATO strap; it is the Sinn most often described as a one-watch collection. The 104's polished case, rotating bezel and day-date dial are unambiguously pilot-watch; it is excellent casual and business-casual, but it never fully disappears into formal wear. Buyers wanting one watch for office, weekend and travel should favour the 556; buyers whose wardrobe is predominantly casual, or who actively want the aviation aesthetic, should favour the 104.
Both use Sellita movements with wide third-party serviceability, identical Sinn warranty terms and the same case-construction standards, so long-term ownership costs are effectively identical. Both list within a similar band at German retail, with the 556 typically the slightly cheaper of the two depending on strap or bracelet configuration — treat any specific figure as a starting point to confirm on sinn.de before buying. This comparison is decided by fit and function, not by money, unlike most two-watch decisions at this level.
Wrist size and how often you would actually use a day-date or a pilot's bezel can produce a clear personal winner even where the editorial verdict is close.
Find which one fits youTen 556 references and seven 104 references are catalogued, sharing the same case sizes and Sellita bases as the two compared here.
No. Beyond 2.5 mm of extra diameter, the 104 adds a day display, a Sellita SW220-1 instead of the 556's SW200-1, a captive bidirectional pilot's bezel, and a polished rather than satinized case. It is a different instrument-watch brief, not a scaled-up 556.
The 556 I, at 38.5 mm and roughly 65 g, is the clear choice under a wrist of about 17 cm. The 104's 41 mm case and polished finish give it more visual weight that reads as large on smaller wrists.
No, they use related but different Sellita calibres. The 556 runs the SW200-1, a date-only movement, while the 104 runs the SW220-1 to drive its added day display. Both beat at 28,800 vph with hacking seconds and DIN 8309 antimagnetic protection.
Yes. Both are rated to 20 bar (200 m) with a screw-down crown and low-pressure resistance, well within swimming use. Neither is marketed as a dive watch, and the 104's rotating bezel is a timing tool rather than a dive-timing bezel.
For most buyers, the 556 I: it is the more versatile everyday watch, the more compact fit, and the cheaper of the two at retail. Choose the 104 St Sa I first only if a day display and a pilot's bezel are features you already know you will use.