Short answer
On a replica Omega Seamaster 300M, "512" is almost never an Omega reference number. It is a batch or version code used by a seller or a factory. Omega's own catalog numbers for the 42mm Seamaster Diver 300M look like 210.30.42.20.03.001, and the brand does not use plain three digit codes for this line. So treat 512 as the name of a production run, then ask the seller what that run actually changed. If they cannot answer, the number is marketing.
Why sellers use codes like 512
The replica scene labels everything. Codes get reused across shops, and two sellers listing the same 512 can ship watches built in different workshops. Sometimes the number tracks a dial color or a bracelet option. Sometimes it tracks a revised case or a new batch of movement plates. It rarely tracks anything you can verify from a photo. I look for a seller who can name the factory, the movement, and the run, because that is the only version of the code with meaning.
The genuine specs you are comparing against
Before judging any replica, know the target. The current 42mm Diver 300M is the reference point for most of these builds.
- 42mm case, roughly 13.6mm thick, 20mm lugs, about 50mm lug to lug
- Ceramic dial with laser engraved waves, date at 6 o'clock with no metal frame
- Helium escape valve at 10 o'clock, conical crown guards, scalloped bezel edge
- Calibre 8800, Co-Axial, Master Chronometer, 55 hour reserve, 15,000 gauss resistance, 300m rating
- Sapphire front and back, anti-reflective coating on the inside
- Blue glowing Super-LumiNova on the hands, markers and bezel pip
What sits inside a 512 build
Most of these watches run a Seagull or Hangzhou clone of the ETA 2824, or a decorated movement that copies the 8800 rotor and bridges. The decoration is cosmetic. There is no Co-Axial escapement and no silicon hairspring, so the magnetic resistance that defines the real 8800 does not carry over. A healthy A2824 clone will keep decent time and give you 38 to 42 hours of reserve. That is a workable watch. It is not the watch on the Omega spec sheet.
Details that give a replica away
Thickness is the usual first tell. Many builds land past 14mm, which pushes the case off the wrist differently than the real thing. Beyond that:
- Crown guards that look slab sided instead of sculpted into the case
- Wave dials that are stamped or printed, so the waves look flat under angled light
- Date font that is too wide, or a window sitting a hair off center
- Bezel insert that clicks loosely and lines up poorly at 12
- Bracelet with pin and collar links, shallow clasp engraving, or no taper
- Lume that glows green, or fades within twenty minutes
Ask for close ups of the crown side, the caseback, and the clasp. Sellers who only send front-on glossy shots are usually hiding something in those three places.
Water resistance and service reality
No replica is pressure tested to 300m, whatever the caseback says. Gaskets vary between batches and crowns are not always seated properly. Do not swim in one, and do not shower in one. Servicing is the other gap. An Omega service center will not touch it, so you are relying on an independent watchmaker who can source parts for the movement inside. Know what movement you have before you need that favor.
Questions worth asking
- Which factory built this run, and what changed from the previous one?
- What movement is inside, and is it a genuine ETA or a clone?
- Can you send photos of the case profile, caseback and clasp?
- What is the measured case thickness?
- What happens if it arrives dead or damaged?
The part listings tend to leave out
Counterfeit branded watches are illegal to import and sell in the United States, and trademark holders can have shipments seized. Reselling a replica as genuine is fraud, plain and simple. Buying one for yourself is a personal call, but go in clear eyed: you are buying a watch with no factory warranty, no service network, and no resale value. Judge it as a piece of hardware at a price, not as a shortcut to the real reference. If the wearer treats it honestly, that is a fine hobby. If the plan is to fool someone, that is a different conversation.