A fake Fifty Fathoms 38mm is a copy of the Blancpain Fifty Fathoms Automatique in its smaller case size, about 38.2 mm across instead of the 45 mm version. Buyers pick this size because it wears closer to a vintage dive watch and fits wrists under 7 inches. The better replicas match the case diameter, the sapphire bezel insert, and the dial layout. Most still get the case thickness, the bezel click, and the movement finishing wrong. The checks below run in the order a watchmaker would use them.
Before You Inspect
Gather the tools first. Without them, every judgment is a guess.
- Digital caliper reading to 0.01 mm
- Scale accurate to 1 gram
- 10x jeweler's loupe
- Bright, indirect light or a diffused lamp
Remove the strap before measuring. A mounted strap adds to the lug-to-lug reading and hides how the spring bars seat.
The Genuine Numbers to Compare Against
Blancpain lists the 38 mm Fifty Fathoms Automatique with a 38.2 mm case, a sapphire crystal, a unidirectional rotating bezel, and 300 m of water resistance. The movement is an automatic from the calibre 1150 family, quoted at 100 hours of power reserve with a silicon balance spring. Those figures are the benchmark. A replica claiming the same reference should land within a fraction of a millimeter on diameter and within about a millimeter on thickness.
Run the Checks in Order
- Measure the case diameter across the 3 and 9 o'clock flanks with the caliper jaws flat against the case sides.
- Measure total thickness from the caseback center to the top of the crystal.
- Weigh the bare watch head and note whether it feels light for a steel case of this size.
- Turn the bezel through a full rotation and count the clicks.
- Examine the dial print and the date window under the loupe.
- Charge the lume with the lamp, then check it in a dark room after 30 seconds and again after 5 minutes.
- Unscrew and reset the crown, then cycle the date through at least 10 days.
- View the movement through the display back and check the finish, the rotor engraving, and the balance.
What the Measurements Tell You
Case diameter is the easiest thing to fake and the least useful. Thickness is where most replicas slip. A copy that runs 1.5 mm thicker than the genuine watch sits high on the wrist and looks wrong from the side, and the extra height often comes from a spacer ring around an undersized movement. Weight is a second signal: a hollow case and a thin caseback read light in the hand.
Bezel, Dial, and Lume
The bezel should rotate with firm, even clicks and stop at each marker with no back play. Loose bezels with a mushy feel are the most common complaint at this size. Dial printing on a good copy is crisp under magnification: the text has clean edges, the markers sit level, and the date sits centered in its window. Lume is the giveaway nobody hides. Apply a light charge and watch how fast it fades. Weak compound fades inside minutes; decent compound holds a readable glow for hours.
Movement Reality Check
Most 38 mm replicas run a decorated Seagull, a Miyota 9015, or a clone of an ETA 2824. These are serviceable movements and keep decent time, but none of them delivers a 100-hour power reserve. Test it: wind the watch full, set it down, and check it at 24, 48, and 72 hours. If it stops on the second day, the specification claim is marketing.
What No Replica Matches
- The silicon balance spring and its resistance to magnetism
- The 100-hour reserve of the genuine calibre
- Hand-applied finishing such as beveled bridges and Geneva stripes done to Blancpain standards
- Factory pressure testing to 300 m, which a replica case has never seen
- Service and parts support from an authorized watchmaker
Care and Limits
Treat a replica as a splash-resistant watch until a watchmaker pressure tests it. Gaskets on budget cases are often dry or poorly seated, and a screw-down crown does not guarantee a seal. Have the caseback gasket changed at service, keep the watch out of hot showers and salt water, and expect a movement service every three to five years. If you plan to dive, use a watch rated and tested to ISO 6425, not a replica.