Short answer
A 43mm Fifty Fathoms reproduction is a Chinese-built copy of Blancpain's diver, sized somewhere between the 45mm Automatique and the 43.6mm Bathyscaphe. The decent ones get the sapphire bezel insert, the domed crystal, the sword hands, and the 4:30 date right. The cheap ones get the case profile wrong and the bezel feels like a jar lid. Budget $250 to $450 for something worth wearing, and never assume it can go in the water.
Why 43mm means different things to different sellers
Blancpain's own catalog does not contain a 43mm Fifty Fathoms. The Automatique 5015 measures 45mm across. The Bathyscaphe sits at 43.6mm. The 70th anniversary pieces came in at 42.3mm and 41.3mm. So when a listing says 43mm, the seller is usually rounding the Bathyscaphe, or describing a case that was made to their own drawing.
Ask for a caliper photo across the case, plus lug to lug and thickness. Thickness is where most reps fall apart. The genuine Automatique is roughly 15mm thick and the Bathyscaphe lands near 14mm. A rep with a stacked date module can hit 16mm and wear like a brick on a 7 inch wrist.
Case, bezel, and the parts you actually touch
The bezel is the first thing I test. Real Fifty Fathoms bezels are unidirectional with crisp detents and almost no back play. A good reproduction gets close: 120 clicks, a sapphire insert with a lume pip, and enough tension that it will not drift during the day. A bad one wobbles and the triangle never lines up at 12.
Fifty Fathoms 43mm Imitator Guide: Specs, Fit, and What to Inspect
Look at the finishing mix. Brushed case flanks, polished chamfers along the lugs, brushed lug tops. If the whole case is one uniform satin blast, it came off a cheaper line. Crown guards should have sharp edges that feel machined, not cast. The crown should be signed and the threads should bite on the first half turn, not the third.
Movements: what is inside
Most 43mm Fifty Fathoms reps run a clone of the ETA 2824-2 or 2836-2. Some use a Seagull ST2130 or a PT5000. A small number carry a decorated automatic shaped to look like Blancpain's calibre 1315. The real 1315 has three barrels, a 120 hour power reserve, and a silicon balance spring. No reproduction has that. What you want is a movement that hacks, hand winds, and holds within about 15 seconds a day. Anything running at 28,800 vph is fine.
Ignore the Swiss made engraving on the rotor. It is cosmetic.
Dial details that give it away
The 5015 has a date at 4:30. Printing should be sharp and correctly spaced, with the brand name in the right serif weight. Lume plots should be applied and level, not painted on. On many reps the date wheel font is too bold or the numerals sit too high in the window.
Hands should be brushed on the top surface with polished bevels, and the sweep seconds hand should reach the minute track instead of stopping short. Under a phone macro shot, dial text is the fastest tell.
What I check before paying
- Bezel action and insert alignment at 12
- Dial printing under a loupe or a macro photo
- Crown threading and stem length
- Caseback engraving depth and serial numbers
- Lume glow after 30 seconds under a light
- Timegrapher numbers, if the seller has one
Water resistance
Assume zero. Even when a listing claims 300m, the gaskets are the cheapest part in the build. A watchmaker can pressure test and reseal it for $40 to $80. Until that happens, keep it away from the pool, the shower, and the ocean.
Price bands
$80 to $150 buys a rough watch with a hollow bracelet. $200 to $300 gets a solid daily wearer with decent finishing. $350 to $500 gets the best case work and a better movement. Past that, you are paying for a name on a rotor.
Bottom line
A 43mm Fifty Fathoms reproduction can be a good watch if you buy for build quality instead of the logo. Measure the case, test the bezel, and treat water resistance as unproven until a professional says otherwise.