The short answer
Patek Philippe does not make a Nautilus reference 6790, and never has. The catalogued Nautilus line runs from the 3700 of 1976 through the 5711, 5712, 5726, 5740, 5980 and 5990, then on to the 5811. The 6790 number sits outside that sequence entirely. It appears in replica listings and in search bars, usually attached to a steel Nautilus style case. So the question worth asking is not how good a "6790" is. It is which real Nautilus the copy is modeled on, and how well the maker executed it.
What the number probably points to
Sellers recycle and remix reference numbers because the numbers pull search traffic. A listing labeled Nautilus 6790 is, in practice, almost always one of two things: a three hander built on the 5711 template, or a chronograph built on the 5980 or 5990 template with the subdials arranged differently. Occasionally you will see the number glued onto an annual calendar style dial to suggest a 5726.
The number itself reads oddly to anyone who follows the brand. Patek's 6xxx block belongs mostly to Calatrava and Grand Complication pieces, and the Nautilus has lived in the 3xxx, 4xxx, 5xxx and now 58xx ranges for decades. That mismatch is a small tell about how much care went into the listing.
What separates a good copy from a bad one
Case and bracelet
The Nautilus case is a soft rounded octagon with a thin bezel, and thickness is where cheap copies fall apart. A 5711 style case measures 40mm across and roughly 8.3mm thick. Decent replicas land between 8.5mm and 9.5mm. Budget ones run 11mm and wear like a brick on the wrist. Ask for caliper photos, not wrist shots.
On the bracelet, the links should taper by degrees toward the clasp, and the brushed flats should stop cleanly where the polished bevels begin. Sloppy finishing shows up as rounded edges and a taper that never changes.
Dial and hands
Under a loupe I look at the date window first. The font is the giveaway on most copies, followed by how well the aperture is cut and whether the wheel sits centered. Then the horizontal grooves, the printing weight on the brand name, and the lume application. Baton hands should be flat and sharp, not domed and soft.
Movement
Most copies run a Miyota 9015 or a Seiko NH35. Both keep time and both are honest about what they are. A decorated Asian ETA clone is a step up in feel. A true clone of the calibre 26-330 SC or 324 S C is rare, and sellers who claim it are often showing borrowed photos. Ask which movement sits inside, then ask for a shot of the caseback with the rotor visible.
What I would ask before paying
- Caliper photos of case width and thickness, crown included.
- Macro shots of the dial, date window and clasp engraving.
- The movement name, not a marketing phrase like "Swiss grade".
- Whether the clasp and bracelet end links sit flush with the case.
- A written return window and a payment method that can be reversed.
The legal side, if you are in the US
Counterfeit watches carrying a live trademark are illegal to import. Customs and Border Protection can seize and destroy a shipment, and trafficking in counterfeit goods is a federal offense. Buying from a domestic seller does not make it lawful. The phrase "Swiss made" in replica marketing describes a label, not a place of assembly, and most watches sold that way are finished in Asia.
Bottom line
If a listing promises a Nautilus 6790, you are looking at invented numbering wrapped around a 5711 or 5980 style case. Judge the watch on measurements, movement and finishing, and treat the reference number as marketing noise.