A fake Fifty Fathoms 43mm is a replica of the Blancpain Bathyscaphe, the roughly 43mm branch of the Fifty Fathoms family, not the 45mm Fifty Fathoms Automatique. The genuine Bathyscaphe case measures about 43.6mm across and 13.8mm thick, houses the in-house calibre 1315, and carries a 300m water resistance rating. Replicas copy that silhouette, but they swap in a Japanese or Chinese automatic movement, so thickness, bezel action, and power reserve become the quickest tells.

Is the 43mm Fifty Fathoms the same as the 45mm Automatique?

No. The Fifty Fathoms Automatique reference 5015 is a 45mm watch at roughly 15.4mm thick, while the Bathyscaphe sits near 43.6mm and 13.8mm thick. Both share the 300m rating and the calibre 1315, a three-barrel automatic with a silicon balance spring and a 120-hour power reserve. Blancpain's 2023 anniversary editions landed at 42.3mm, which is why catalog listings often blur the 42mm, 43mm, and 45mm numbers together.

Why do replica makers build the 43mm size?

The 43mm Bathyscaphe is the most wearable modern Fifty Fathoms, so it is the version most often copied. A 43mm case also takes an off-the-shelf automatic movement plus a spacer ring without looking oversized on the wrist. That combination keeps replica production cheap while matching a case diameter buyers can actually wear daily.

How do you spot a fake 43mm Fifty Fathoms?

• Case thickness: replicas usually run 14.5mm to 15.5mm because of the movement spacer. Measure with calipers, not by eye.
• Bezel action: the genuine unidirectional bezel turns in 120 crisp clicks with no back play and the triangle locks at 12.
• Date at 4:30: the window angle, font, and date wheel alignment are common weak points on copies.
• Crystal coating: genuine sapphire carries double anti-reflective coating, so it nearly disappears. Fakes often show a blue or green reflection.
• Caseback and movement: look for engraving depth, serial formatting, and a decorated rotor. Replica decoration rarely matches the calibre 1315's architecture.
• Lume: applied indexes should glow evenly and brightly, not dimly or with a greenish cast.

Does a replica keep the 120-hour power reserve?

No. Most 43mm replicas use a Miyota 9015 derivative rated near 42 hours or a Seagull ST2130 near 38 to 40 hours. The genuine calibre 1315 runs three mainspring barrels in series for a full 120 hours, meaning it still runs after five days off the wrist. Take a replica off on Monday and it will be stopped by Wednesday.

What do 43mm Fifty Fathoms replicas cost?

Entry replicas sell for about $150 to $250, mid-tier versions for $300 to $450, and the better-built examples for $500 to $800. Price tracks the movement finish, bezel insert material, anti-reflective coating, and strap quality. A low price paired with claims of a genuine-style 120-hour movement is a clear warning sign.

What should you verify before buying one?

• Water resistance. Ask for a pressure test result and never dive or swim with a replica.
• Measured dimensions. Request caliper photos of diameter and thickness.
• Servicing. Many independent watchmakers decline to work on replica movements.
• Lug width. The 43mm Bathyscaphe uses 23mm lugs, so genuine or aftermarket straps only fit if that measurement matches.

Does a 43mm replica Fifty Fathoms take genuine straps?

It can, if the lug width is a true 23mm and the spring bars sit at the correct depth. Many replicas measure 22mm or 24mm instead, which leaves gaps at the lugs. Measure the lug opening before ordering a strap.