The Short Answer
512 is not an Omega reference number. It is a seller-side batch tag. Replica sellers group Seamaster Diver 300M builds into numbered runs so buyers can compare one lot against another. A 512 listing usually means a 42 mm steel case, a ceramic-look bezel insert, a wave-textured dial, and a choice of automatic movement. The real Omega reference for the same watch looks like 210.30.42.20.03.001, and that number appears on the genuine case back and on the warranty card.
Before You Start
- A clear photo set of a genuine 42 mm Seamaster Diver 300M for side-by-side comparison
- A 10x loupe
- Digital calipers
- A rubber case-back ball or a two-prong opener
- A small digital scale
- A phone with macro mode and steady lighting
Step-by-Step Inspection
- Measure the case width across the lugs at 10 and 4 o'clock. A 512 batch should read 41.8 to 42.2 mm. Anything under 41.5 mm is a smaller case body sold under the same tag.
- Measure the thickness from case back to crystal top. Expect about 13.5 mm with an automatic movement. A quartz build lands closer to 11 mm and sits flatter on the wrist.
- Check the helium escape valve at 10 o'clock. On a well-made batch the crown sits flush, the cone shape is even, and the logo engraving is centered. A crooked valve or a loose cone is the fastest tell on this case style.
- Inspect the bezel insert. Genuine ceramic has a deep, uniform black or blue with enamel-filled markers and a lume pip under a sapphire cap. Replica inserts often show a milky edge or a pip that looks painted.
- Turn the bezel through a full rotation and count 120 clicks. Gritty action, back play, or a misaligned 12 o'clock triangle points to a low-grade ratchet ring.
- Photograph the dial under raking light. The wave pattern should be cut with sharp crests. Printed or stamped waves look flat and blur where the light crosses them.
- Compare the date window. Genuine windows are polished and slightly beveled. A raw punched edge with white adhesive showing is a common flaw on cheaper batches.
- Check hand length and lume. The seconds hand should reach the minute track. Skeleton hands should have clean borders with no paint bleed.
- Weigh the head and bracelet separately. A full steel bracelet in this style usually lands near 100 to 110 g on its own. Light bracelets use hollow center links and thin end links.
- Open the case back with the rubber ball. Note the movement ring, rotor engraving, and any plastic spacer. A decorated clone with a printed rotor is normal at this tier. Exposed glue or a loose ring is not.
- Time the movement on a phone app or timegrapher in four positions. Healthy readings sit between minus 10 and plus 15 seconds per day with an amplitude above 250 degrees. Wild swings between positions mean a worn or unregulated movement.
- Skip the water test unless the gaskets were replaced and greased by a watchmaker. A seller claim of 300 m does not transfer to a replica case.
What the 512 Tag Does Not Tell You
The tag covers a case and dial run, not a single build. Two watches from the same batch can ship with different movements, different bracelets, and different crystals. Ask for movement photos and a bracelet photo before you compare anything to the tag. Sellers also reuse popular batch numbers after a mold change, so a 512 sold this year may not match a 512 sold two years ago.
Legal and Practical Limits
Counterfeit watches are illegal to import and sell in the United States. US Customs and Border Protection seizes shipments and can destroy them, and the buyer absorbs the loss. No replica carries a factory warranty or a valid serial number, and most service centers refuse to work on them. Treat every specification in a listing as a claim to verify, not a fact.