Short answer
"Calibre" is a movement name. It is not a size. The 39mm in a listing describes case diameter. A watch sold as "fake calibre 39mm" is a replica with a 39mm case and a movement the seller labels with a calibre name. No standards body defines a "Calibre 39." The label comes from the seller, not from a manufacturer.
What 39mm measures
Case diameter is measured across the case at its widest point, with the crown left out. A 39mm case sits between a 36mm dress watch and a 42mm dive watch. It fits wrists from about 16cm to 18cm. Lug-to-lug length and case thickness matter as much as the diameter. A 39mm case with 50mm lugs wears larger than a 40mm case with 46mm lugs.
Where the calibre name comes from
Watch brands use "calibre" for their own movement numbers. Examples: Omega 8800, Rolex 3230, Cartier 1904-CH MC, Seiko 6R35. These numbers are brand property. Replica sellers copy them into product titles. Under the decal, the movement is a different part. Common units in replica cases: Seagull ST21, Hangzhou 6300, Miyota 9015, or a quartz module. A seller who cannot name the movement cannot describe the watch with accuracy.
Checks before payment
- Ask for a caliper photo across the bezel, dial side up.
- Ask for a movement photo with the rotor turned aside.
- Compare thickness against the genuine spec sheet. Replicas run 1mm to 2mm thicker in most cases.
- Ask for the caseback reference and the serial format, not the serial number.
- Treat water resistance claims as unverified. Few replica cases pass ISO 22810 testing.
US legal position
Trafficking in counterfeit goods is a federal offense under 18 U.S.C. § 2320. A first conviction carries up to 10 years in prison and a $2 million fine for an individual. U.S. Customs and Border Protection seizes counterfeit watches at ports of entry. A replica has no manufacturer warranty and no parts network. Resale value is near zero.