Quick answer
Fake Omega Seamaster 300 41mm watches fail on measurements more than on looks. The real Seamaster 300 case is 41mm wide. Lug width is 21mm. Water resistance is 300m. Reference 234.30.41.21.01.001 uses the Master Chronometer calibre 8912. A copy that carries a 20mm strap, a 42mm case, or a Miyota movement is not close.
Which watch this keyword points to
Omega sells two watches near this size. Replicas of both exist.
- Seamaster 300: 41mm case, heritage dial, conical crown, no helium escape valve. Ref 234.30.41.21.01.001 (2021, calibre 8912). Ref 233.30.41.21.01.001 (2014, calibre 8400).
- Seamaster Diver 300M: 42mm case, helium escape valve at 10 o'clock, wave dial, date at 6.
A listing that says Seamaster 300 41mm but shows a helium valve at 10 o'clock is a Diver 300M, real or not.
Case and measurements
Measure with a caliper, not a photo.
- Diameter: 41mm at the bezel edge. Copies run 42mm to 43mm.
- Lug width: 21mm. A 20mm or 22mm spring bar will not seat.
- Lug to lug: about 48mm.
- Thickness: about 13.9mm with the domed crystal.
- Crown: conical, no crown guards.
Dial and hands
The 2021 Seamaster 300 uses a sandwich dial. The index cutouts sit in a lower plate and hold vintage tint Super-LumiNova. Copies print the indexes on one flat surface, or use lume that reads white or green under a phone light. The seconds hand has a lollipop tip. The arrow hour hand and sword minute hand have polished bevels on the real parts. Fake hands show a stamped edge and flat paint.
Bezel and crystal
The bezel insert is black ceramic. The dive scale is white enamel. It fills the engraved track and sits flush. Fake inserts show a decal edge, uneven fill, or a bezel that turns with grit and back play. The crystal is domed sapphire with antireflective coating on the inside. A mineral glass or low grade sapphire shows a blue or purple haze at an angle.
Caseback and movement
Ref 234.30.41.21.01.001 has a sapphire caseback. The calibre 8912 shows twin mainspring barrels, a free-sprung balance, a silicon hairspring, and Arabesque Geneva stripes. The rotor carries the Omega name and the Master Chronometer text. Copies use a Miyota 9015 or a Chinese 8215. Signs of a copy: one barrel, a regulator arm with a screw, a glued rotor plate, or a closed caseback on a reference that should be open.
Serial numbers and paperwork
Omega stamps an 8-digit serial on the lug at 7 o'clock. Reference numbers have the form 234.30.41.21.01.001. The serial and reference should match the card, the caseback, and the movement. Master Chronometer watches ship with a card that holds a test code. Omega's site has a lookup for that code. A card with no test result is a card from a copy.
Price check
Genuine Seamaster 300 41mm watches trade near $4,000 and up on the used market. Replica listings sit between $250 and $900. A seller who asks $1,200 for a new one is selling a copy with a markup.