The short answer
Rolex never produced a Sea-Dweller with the reference number 16666. That number does not appear in any Rolex catalog, service manual, or parts list, and no genuine example left the factory with 16666 stamped between the lugs. When you see a listing or a forum post using 16666, the number is either a typo or an invention. The references people almost always mean are 16660 and 16600.
What 16666 usually stands for
Two real references sit one digit away from the made up number, and both are common in the replica market because they look similar at a glance.
- 16660: the "Triple Six," launched in 1978. It replaced the 1665 and raised the depth rating to 1,220 meters (4,000 feet) with a larger helium escape valve.
- 16600: the successor, introduced in 1988. Same 40 mm case and 1,220 meter rating, but updated with the caliber 3135 and a sapphire crystal.
- 1665: the earlier "Double Red" Sea-Dweller, rated to 610 meters and produced before the 16660.
If a seller types 16666, ask which of those three they actually have. A vague answer tells you more than the photos do.
Why a 16666 listing is a warning sign
Someone handling a genuine Sea-Dweller reads the reference off the case many times. A seller who cannot get five digits right is unlikely to have verified anything else about the watch.
- Stock photos used across multiple listings under different numbers.
- No photo of the case between the lugs, where the reference is stamped.
- Papers or a warranty card that lists a number different from the case.
- A price far below the current market for a 16660 or 16600.
How to confirm a Sea-Dweller reference number
- Remove the bracelet with a proper spring bar tool and read the stamp on the case between the lugs at the 12 o'clock side.
- Compare that stamp against the model number printed on the warranty card or certificate.
- Check the dial text: a 16660 uses tritium or later luminova markings, while a 16600 runs to the end of production with superluminova.
- Look at the caseback engraving for the correct Rolex wording and depth rating for that reference.
- Measure the case with calipers. Both references are 40 mm wide with a 20 mm lug width and roughly 15 mm thick.
- Have a watchmaker open the case and identify the movement. A 16660 should carry a caliber 3035 and a 16600 a caliber 3135.
Where replica Sea-Dwellers fail inspection
Most 1:1 replicas of this model are built from a 16600 base and sold under whatever number moves stock, which is how "16666" ends up in titles. Under a loupe, the usual tells are the helium escape valve threads, the font weight on the bezel insert, the date wheel font and magnification, and the crown guard shape. Genuine cases have crisp lug chamfers that replica machining tends to round off, and the lume plots on older tritium dials age to a warm cream that replica paint does not match.
Buying, selling, and the law
In the United States, importing or selling counterfeit goods is illegal, and items can be seized by customs. Buying a replica for personal use carries its own risk of loss, and reselling one as genuine is fraud. If you are researching a watch, treat the reference number as the first check and never accept a listing that cannot show it clearly.