The short answer
A fake Fifty Fathoms 38mm is a replica of Blancpain's small-case diver, usually the Fifty Fathoms Automatic 38mm (ref 5100B) or the Bathyscaphe Automatic 38mm. The 38mm size is the part that trips people up. Most replica volume sits in the 45mm Fifty Fathoms, so the 38mm versions come from fewer factories, get less attention, and vary a lot from batch to batch. If you know the real dimensions and finishes, the tells show up fast.
Know the real watch first
You cannot judge a replica without the numbers it is copying. The 38mm Fifty Fathoms family shares a basic recipe:
- Case listed at 38mm, measured closer to 38.3 to 38.6mm depending on reference, with a lug width of 20mm.
- Thickness around 10 to 11mm, thin for a 300m diver and one of the hardest things to fake well.
- Calibre 1150 inside, a twin-barrel automatic with a 100-hour power reserve and a gold rotor.
- Sapphire bezel insert on the Fifty Fathoms, ceramic with Liquidmetal markers on the Bathyscaphe.
- Sapphire caseback with engraved reference and serial details on the case and rotor.
Those five points cover most of the arguments about a fake.
Where replicas win and lose
Bezel and crystal
The real bezel insert is sapphire, thick, with a lume pip set into a recess. Replicas often use mineral glass or a thin sapphire disc with a printed pip. Turn the bezel: the real one clicks with sharp, even detents and no back play. Plenty of fakes feel gritty, or the pip sits a fraction off 12.
Case and lugs
Look at the brushing. Real 38mm cases have crisp brushed top surfaces with a polished bevel along the lug edges. A fake usually over-polishes those edges until they look soft. Check the lug width too: a rep that takes 21mm straps is not a 38mm Fifty Fathoms case, whatever the listing says.
Dial and hands
Printing on the real dial is fine and matte. On fakes the text is often too heavy, the date font too bold, or the date window sits slightly low. Hands should be polished with clean edges and Super-LumiNova that glows the same tone as the markers.
Movement
This is the honest part. Most 38mm replica Fifty Fathoms run an ETA 2824 clone, a Miyota 9015, or a decorated Chinese automatic dressed to look like a 1150. None of them deliver a 100-hour reserve. Wind it, set it down, and check it 48 hours later. If it still runs, someone did something interesting. If it stopped, you have a 38-hour movement behind a rotor stamped to look like something else.
In-hand checklist
- Measure the case with calipers, not the listing.
- Check the lug width with a strap gauge.
- Time the power reserve over two days.
- Look at the bezel pip under a loupe.
- Compare caseback engraving depth and font with reference photos.
- Weigh it. Real steel 38mm cases land in a narrow range, and hollow or plated cases feel light.
Water resistance and daily wear
Real Fifty Fathoms are rated to 300m and tested one by one at the factory. Replicas are not. Seals may be fitted, but nobody pressure tests them, so treat any 38mm fake as splash resistant at best. Showering, swimming, and diving are how these watches die.
Before you buy
Counterfeit sales are illegal in the US, and customs can seize a package. Buying for personal use is a different question than selling, but the risk sits with you either way. If the goal is the look of a small dive watch, plenty of legal homage pieces use the same proportions. If the goal is the real thing, the secondary market is the only place to find one.