The short answer, before the long one
I have handled both sides of this comparison more times than I can count, and the surprise is never the case shape. A high-tier replica of this reference gets the silhouette right, the weight convincing, and the bracelet feel close enough that you stop noticing it after ten minutes. What it cannot match is dial printing under magnification, the movement, and the way a genuine case ages around its edges.
So my pick for anyone asking the vs real question is blunt: if the reference itself matters to you, buy the real watch. If you only want the look on your wrist, buy the best replica tier you can actually verify, not the cheapest one with photos of a genuine piece.
What "1666/6" actually refers to
Search Rolex's published reference lists and 1666/6 does not come back as a standalone model. The string shows up in the replica market as seller shorthand, borrowed from the five-digit Submariner and Sea-Dweller family. That means the underlying debate is the same one you have with a 16610, a 16613, or a 16660: vintage proportions, aluminum bezel, drilled or non-drilled lugs depending on the year, and a movement from the 3135 or 1570 line.
If a listing insists 1666/6 is a factory code, treat that as a signal. Real references come with paperwork and a service history you can trace. Marketing numbers do not.
Side by side: the tells that decide it
- Dial printing. Genuine text sits crisp with sharp serifs and even spacing between the coronet and the model line. Replicas blur at the edges and space the words wrong, often with an S that leans.
- Cyclops and date. Real magnification is 2.5x, and the date font is thin and centered. Fakes run large, and the date sits low or washes out at an angle.
- Case and crown guards. Genuine guards slope into the case with a soft curve. Replicas leave a hard shelf, and the lug tips look chunky from above.
- Bezel insert and pearl. The pip on a real insert sits flush in a metal ring. On replicas it is a plastic dot set too high, and the numerals behind it are printed, not anodized.
- Bracelet and end links. Real end links seat tight with no play and no light gap. A fake rattles, and the clasp stamping looks pressed rather than cut.
- Movement. This is the separation point. Genuine calibers beat at a steady rate with smooth sweep, and the winding feels grainy in a good way. Replica movements feel sandy and lose time within a week.
- Caseback and rehaut. Engraving depth on a real caseback is even and shallow. Fakes machine it deep and sharp. Rehaut lettering on a replica rarely lines up with the minute markers.
- Weight and sound. A genuine five-digit Sub lands around 130 to 150 grams depending on configuration. Replicas miss that number, usually light, and they ring when tapped.
Options, ranked by what you actually get
Tier one: top-grade replica with a known movement
This is the only replica tier I would consider. You want a seller who names the movement, shows a timegrapher reading, and posts macro photos of the dial rather than studio renders. Expect solid end links, a decent insert, and a watch that keeps time within a few seconds a day. It will still fail the dial and cyclops tests in person.
Tier two: mid-tier replica
Pass. The case profile drifts, the bracelet feels hollow, and the crystal sits wrong. You save a little and lose the whole point of the exercise, which is a watch that reads correctly from a foot away.
Tier three: the genuine article
A real five-digit reference costs more, holds value, and can be serviced for decades. If you are comparing because the reference means something to you, this is the answer, and no replica tier changes it.
How I vet a listing
- Ask for a wrist shot in daylight, not a lightbox photo.
- Ask for the movement name and a timegrapher screenshot with a date.
- Check whether the seller uses the same photos across multiple listings.
- Pay only through a method with buyer protection, and read the return terms first.
Bottom line
Fake Rolex 1666/6 listings win on price and nothing else. They get you the shape. They do not get you the dial, the movement, or the aging. Buy the real thing if the reference matters, and if you go replica, buy the top tier or skip it.