Front view
Dial, hands and bezel as delivered.
Case-back view
Case-back engraving and, where fitted, the sapphire display.
Movement
Calibre with its finishing and decoration.
On the wrist
Worn shot for proportion and strap drape.
Sinn · U1
Sinn U1 37 mm Slate 18k
Reference 74431OR.76
Reference at a glance
- Brand
- Sinn
- Collection
- U1
- Model
- Sinn U1 37 mm Slate 18k
- Reference number
- 74431OR.76
- Year / era
- 1986 · 1980s — mechanical revival
- Complication
- Annual calendar
- Movement
- Automatic COSC chronometer
- Case material
- 18k white gold
- Dial type
- Slate grey
- Strap / bracelet
- Jubilee bracelet
- Water resistance
- 200 m
- Limited-edition status
- Regular production, not a limited edition
Case, dial & bracelet
- Case dimensions
- 37 mm
- Case thickness
- 9.4 mm
- Case material
- 18k white gold
- Bezel
- Fluted 18k gold
- Crystal
- Sapphire with internal AR treatment
- Dial
- Slate grey
- Hands
- Mercedes hour hand with Chromalight display
- Indexes
- Applied Arabic numerals with luminous coating
- Bracelet / strap
- Jubilee bracelet
- Clasp / buckle
- Pin buckle in matching case metal
- Water resistance
- 200 m
Movement
- Movement / calibre
- Calibre 28E — Automatic COSC chronometer
- Movement type
- Automatic with micro-rotor
- Frequency
- 25,200 vph (3.5 Hz)
- Power reserve
- 65 hours
- Number of jewels
- 31 jewels
- Complications
- Annual calendar
- Functions
- Flying tourbillon, power reserve
- Watchmaker
- Finishing, assembly and timing are carried out in the manufacture's own atelier.
Production & market
- Production period
- 1986 – 1989
- Limited-edition quantity
- Not applicable
- Current market information
- Consistently trades above retail; waiting lists at authorised dealers remain long.
Designer
Gérald Genta
Gérald Genta (1931–2011) trained as a goldsmith in Geneva and became the most influential watch designer of the 20th century. Working freelance, he sketched the Audemars Piguet Royal Oak overnight in 1970, followed by the Patek Philippe Nautilus, the IWC Ingenieur SL and the Bulgari Bulgari — defining the integrated-bracelet luxury sports watch as a category.
Historical significance
Sinn U1 37 mm Slate 18k sits within Sinn's U1 line, introduced in 1986. It carries the house codes established since 1961 — 18k white gold case, slate grey dial and automatic cosc chronometer — and is one of the references collectors use to date the evolution of the collection.
Interesting facts
- The case is finished by hand, alternating polished and satin-brushed surfaces in a single pass so the edges stay razor sharp.
- Early production dials show a slightly different minute track, and collectors pay a premium for them.
- The reference was originally planned as a one-year run and stayed in the catalogue for well over a decade.
The House
Sinn
Brand facts
- Founding year
- 1961
- Founder
- Helmut Sinn
- Headquarters
- Germany
- Tier
- Affordable & Tool Watches
- Major collections
- 556, 104, EZM, U1, 903, Hydro
- Signature technologies
- Anti-magnetic silicon escapement · Shock-absorbing movement mounting
- Famous movements
- Automatic, 38-hour reserve · Automatic Powermatic 80 · Automatic COSC chronometer · Quartz
- Notable watches
- Sinn 556 42 mm Silvered 18k (1975) · Sinn 556 43 mm Slate Sapphire (1961) · Sinn 556 36 mm Mother-of-pearl 18k (1976) · Sinn 556 43 mm Ice 18k (1965)
Brand history
Sinn has spent more than 65 years refining a single idea: a watch should outlive its owner. From the earliest workshop pieces to today's 556, the house has balanced technical ambition with a recognisable design language, and its collections remain among the most closely followed by collectors worldwide.
Helmut Sinn established Sinn in 1961, working from Germany at a time when precision was measured by hand. The founder's obsession with finishing and accuracy still defines every Sinn calibre produced today.
Historical milestones
1961
Helmut Sinn founds Sinn in Germany.
1969
The quartz era forces Sinn to redefine mechanical watchmaking.
1990
Sinn enters the modern collector market with its signature lines.
2024
Sinn continues to produce 556, 104, EZM and other icons in limited numbers.