Short answer: there is no Rolex 1666
Rolex has never issued a case reference 1666. If you found a listing built on that number, the seller either mistyped something or made it up. The numbers actually in circulation are 16610 (Submariner Date), 16600 and 16660 (Sea-Dweller), and 1665 (the vintage Sea-Dweller collectors call "Double Red"). The trailing 6 in your search almost always points to something else: the laser-etched coronet at the 6 o'clock position on the crystal. That tiny mark is one of the most commonly advertised features on replicas, which is how a case number and a crystal feature end up mashed into the same phrase.
What the "6" at the end usually refers to
Modern Rolex sapphire crystals carry a faint coronet etched at 6 o'clock, visible only when you tilt the watch under light. Replica sellers like to list it as a specification, the way they list movement type or case size. So a listing that reads "1666 6" is usually a case number with a crystal note attached, not a real model.
That detail matters for dating. A genuine 16610 built before roughly 2002 won't have the etched coronet at all. If a seller claims an early Submariner has one, either the crystal was swapped or the case is a replica.
Why the reference number matters before you pay
Reference numbers tell you the case size, the movement, the water resistance and the bracelet fitted from the factory. Get the number right and half your questions answer themselves. Get it wrong and you end up comparing a 40mm Submariner against photos of a 44mm Deepsea. I see this constantly with buyers who searched the wrong digits.
- 16610: Submariner Date, 40mm, date at 3 with cyclops, 3135 movement
- 16600: Sea-Dweller 4000, 40mm, no cyclops, helium escape valve
- 16660: earlier Sea-Dweller 4000, similar case, older movement
- 1665: vintage Sea-Dweller, 40mm, no cyclops, now a serious collector piece
The checks worth doing
Start with the case profile in your hand. Crown guards on a 16610 taper in a way replicas rarely match, and the lug lines stay crisp rather than soft. Next, check the engraving between the lugs at 12 and 6. Genuine stamps are cut deep and even. Replicas often look shallow, off-center, or stamped into a brushed surface that shouldn't have marks there.
Then look at the dial and hands together. The coronet shape, the font on "SUBMARINER", and the lume color should match the hands exactly. Mismatched lume is the single most reliable tell I know of. On the movement side, a genuine 3135 runs at 28,800 vibrations per hour, sets smoothly, and the date flips clean and centered in the window. Clones can look right on a timegraph and still feel gritty when you set them.
Finally, weigh it. A genuine 16610 on a 93150 bracelet sits around 130 grams. If the watch feels light or the end links rattle against the lugs, keep asking questions.
Red flags in "1666" listings
- The listing never states a case size or movement caliber.
- Photos are stock images or heavily cropped to hide the case sides.
- The price sits far below the market for a complete watch with box and papers.
- The seller claims a laser-etched coronet on a pre-2002 reference.
- "Swiss made" text is smeared or the minute track prints overlap the dial edge.
If you are shopping a replica instead
Be clear about what you want. A good replica of a 16610 should have a 40mm case, a 3135-style movement with a proper date change, a 2.5x cyclops with anti-reflective coating underneath, and solid end links that seat flush. Skip anything advertising "1:1 Swiss 1666" language, since it signals the seller doesn't know the reference either. Buy it as a watch you enjoy wearing, not as an asset, because no replica holds value.
Bottom line
There is no fake Rolex 1666 because there is no real one. Match the digits to a genuine reference first, 16610 or 16600 most likely, then run the case, engraving, dial and movement checks against that specific model. Knowing exactly what you're looking at beats any single tell someone posts online.