Short answer: the genuine Omega Constellation Globemaster is a 39mm watch. There is no 40mm version in the catalog. So when a listing advertises a "fake Globemaster 40mm," you are looking at one of three things: a 39mm replica measured across the crown guards, a replica of the 41mm Globemaster Annual Calendar, or a seller rounding up because 40 sounds tidier than 39. Figure out which one it is before you send money.

Why the 40mm number keeps appearing

Sellers measure cases in different places. Some include the crown, some measure across the widest point of the caseback, and plenty just copy a number from a wholesale sheet and never touch a caliper. A replica with a 39mm movement ring and a slightly padded mid-case can hit 39.8mm on a bench and get listed as 40mm on a product page. That is not always a lie, but it does tell you the seller is repeating specs rather than handling the watch.

The one real exception is the Globemaster Annual Calendar, which Omega builds at 41mm. Replicas of that model exist but are far less common, and most of them get listed at 41mm, not 40. If a listing insists on 40mm and shows a plain date window at six o'clock, it is almost certainly a 39mm copy of the standard three-hand model.

What the real Globemaster does that replicas struggle with

Omega did not make this an easy watch to fake well. A few details carry most of the weight:

• Pie-pan dial. Twelve angled facets meeting at a raised center. Replicas often get the angle slightly wrong, which shows as uneven light reflection across the dial rather than a clean twelve-sided star.
• Fluted bezel in tungsten carbide. Hard material, cut fluting. Copies use polished steel, so the flutes look softer and pick up scratches within weeks.
• Movement. Genuine watches run a Co-Axial Master Chronometer calibre 8900 or 8901, METAS certified, rated to 15,000 gauss. Replicas use a Miyota 9015, a Seagull ST21, or a decorated ETA clone. No certification, no Master Chronometer card that means anything.
• Caseback. Eight stars and the Observatory medallion, engraved deep and crisp. On copies the medallion is usually stamped shallow or laser-etched flat.
• Date and dial text. The framed date at 6, the font weight of "Constellation," and the spacing of the wordmark. Small type is where replica dial printing falls apart first.

How I would read a listing

Skip the marketing photos. Ask for a caliper shot on the actual watch, a clear movement photo with the rotor off-center, and a straight-on dial shot in daylight. Then check these:

• Does the seller say plainly that it is a replica? If not, walk.
• Is the stated size backed by a photo, or only by text?
• Does the bracelet have the correct taper and a clasp with crisp engraving?
• Is water resistance claimed but never tested? Assume splash-only.

Legality and service, the part people skip

Importing counterfeit goods into the United States is illegal, and U.S. Customs and Border Protection can seize the shipment. Selling a replica while presenting it as genuine is fraud, full stop. Omega will not service a counterfeit, and independent watchmakers often decline because parts do not interchange with genuine components. Resale value on a replica is effectively zero, so treat the money as spent the moment it ships.

Bottom line

If you want a 40mm watch, buy a 40mm watch. The Globemaster is a 39mm design, and a listing that fudges that number is telling you something about how carefully the rest of the description was written. Measure claims, movement photos, and honest labeling matter more than any single spec sheet.