Short answer
A fake Patek Philippe 3700/11 is almost never a modern factory replica. The 3700/11 is a vintage reference from the late 1970s and early 1980s, and the big factories that churn out Nautilus copies spend their tooling on the 5711 and 5811 instead. So when a "3700/11" turns up for sale, it is usually one of three things: a real watch with a swapped dial or movement, a modern Nautilus copy being sold under an old reference number, or a cheap vintage-style fake with a printed dial and a generic automatic inside. Sorting out which one you have takes a loupe, a caliper, and about five minutes.
What the reference actually is
Gérald Genta drew the Nautilus in 1976, and the 3700 was the first one out of the gate. It is the Jumbo: roughly 42 mm across, about 7.6 mm thick, steel or gold, with a case that reads wider than it measures because the lateral ears flare out past the bezel. Those ears are part of the case itself, not separate lugs, and the whole thing is built as a monobloc, which is why genuine examples still sit flat and thin on the wrist after forty-plus years.
Inside is the calibre 28-255 C, an ultra-thin automatic that Patek built on the Jaeger-LeCoultre 920 ebauche, the same base that Audemars Piguet turned into the 2121 and Vacheron Constantin into the 1120. It runs at 4 Hz, carries a gold rotor, and is finished well enough to look at through the case back. The dial has horizontal grooves pressed into the metal blank rather than printed on top of it, a date at 3, and the maker's signature under 12. The /11 suffix on the reference relates to the bracelet and clasp revision, so two watches with the same dial can carry different numbers.
The four tells that matter
1. Case thickness and profile
Put calipers on it. The 3700 is a thin watch, and thickness is the hardest thing for any copy to fake without spending real money on a movement. Most fakes land between 9 and 10.5 mm because they are stuffed with a Miyota or a cheap Chinese automatic. Also look at the ear geometry: on the genuine case the ears are crisp, sit proud of the bezel line, and the satin finish on top runs into a polished bevel with a hard, clean edge. Copies soften that transition.
2. The dial grooves
Genuine grooves are dimensional. Tilt the watch under a lamp and you should see shadow and highlight shift along each ridge. A fake dial is flat printed or stamped shallow, so the grooves look painted on and the light barely moves. Check the date window too, since a lot of fakes cut it a hair off axis with the 3 o'clock marker. Lettering is the other giveaway: the fonts are thin and even on original dials, and thick or crowded on copies.
3. The movement
Ask for a photo of the movement before you commit. A 28-255 C has a gold rotor with engraved text, Geneva stripes on the bridges, and perlage on the plates. If you see a bare rotor, no engraving, or a balance wheel that looks like it came out of a $40 movement, the watch is not what the seller says it is. A franken usually shows up here first, with a genuine case and a service movement of a different calibre bolted in.
4. Bracelet, clasp and case back
The integrated bracelet tapers correctly on an original, links move without slop, and the clasp is stamped cleanly. Case back engraving should be sharp and shallow, not laser-deep and rounded. Reference and movement numbers should exist and, ideally, line up with what the seller claims about the watch's history. Many vintage Patek crowns carry no logo at all, so a plain crown proves nothing either way. Do not use that as your test.
Why real 3700/11 copies are scarce
The replica industry follows demand, and demand sits on the current-production Nautilus. A 3700/11 copy would need a thin automatic movement, a monobloc-style case with correct ear proportions, and an embossed dial. That is expensive tooling for a watch most buyers cannot name. What you actually run into at low price points are older fakes from the 1980s and 1990s with quartz or basic automatic movements, and modern listings that use "3700/11" as a label on a 5711-shaped copy.
Questions I would ask before paying
- What is the measured case thickness, in millimeters, with the calipers in the photo?
- Which movement is in it, and can you show the rotor and bridges?
- Are the dial grooves embossed into the blank or printed?
- Is the case back engraving original, or has it been re-cut?
- Has the dial, crystal or bracelet ever been replaced, and by whom?
If a seller dodges the thickness question or sends stock photos of a different watch, that is your answer. The reference is rare enough that any honest listing will have detail shots, and any experienced seller already knows why you are asking.
One legal note
In the United States, selling a watch that carries a counterfeit trademark is illegal, and buying one for personal use sits in a gray area that varies by state and circumstance. That is a legal question rather than a watch question, but it belongs in the same conversation as the price tag.