Short answer
There is no Rolex reference 16666. That number does not appear in Rolex catalogs, auction archives, or service records. Anyone selling a "Sea-Dweller 16666 replica" is either transposing the digits of the 16660, working from a typo for the 16600, or making up a number because it sounds rare. Whatever the listing says, the watch in the photos is a Sea-Dweller 4000 shape, so that is what you should judge it against.
Which references the 16666 is probably standing in for
- 1665 (1967 to roughly 1978). The first Sea-Dweller with a helium escape valve, rated to 610 m / 2,000 ft, acrylic crystal, "SEA-DWELLER SUBMARINER 2000" on the dial. Sold as the Double Red and later the Great White.
- 16660 (1978 to about 1988). Known as the Triple Six. Sapphire crystal, 1,220 m / 4,000 ft rating, helium valve, caliber 3035. This is the reference whose digits get scrambled into 16666 most often.
- 16600 (1988 to 2008). Caliber 3135, the same 40 mm case and 1,220 m rating, and the longest production run of the family. It is also the most common base for replicas, because so many were made.
One detail worth memorizing before you shop: none of these have a cyclops lens over the date. If a listing shows a magnifier on the crystal, the build started from a Submariner parts set and nobody corrected it. That single check filters out a lot of junk.
How to Spot a Rolex Sea-Dweller 16666 Imitation
What to inspect on any replica in this family
I look at these in order, because the first two cannot be fixed after the fact.
The Ultimate Guide to Rolex Sea-Dweller 16666 Replica Models
- Case proportions. 40 mm across, roughly 15 mm thick. Replicas often run thick, or the caseback domes out further than the original does.
- Helium escape valve. It sits at 9 o'clock on the case flank, level with the crown. A printed circle, or a valve set off center, is a giveaway.
- Bezel. Aluminum insert, unidirectional, knurled edge. The first 15 minutes should carry minute graduations, the insert should sit flush, and the pip should line up at 12.
- Dial print. Check the letter spacing in "SEA-DWELLER," the depth rating line, and the weight of the "ROLEX" text. On most replicas the print is slightly too bold or sits too low.
- Crystal. Flat sapphire, no magnification window.
- Movement. Originals ran the 3035 and then the 3135. Most replicas use an ETA 2824 or 2836 clone. Watch the date change at midnight and feel how the crown engages when setting.
- Bracelet and clasp. End link fit at the lugs is where budget builds rattle. A solid feel and a firm click on close matter more than the stamping on the clasp.
What a replica will not do
It will not survive 1,220 m. Even a well-built replica with a screw-down crown and caseback has not been pressure tested to the original spec, and gaskets on budget builds fail early. If you plan to swim with it, have a watchmaker test it first, or just take it off. Rolex will not service or authenticate a counterfeit, and any authorized dealer who opens the case will tell you exactly what it is. Resale value is close to zero, so treat the money as spent on a look rather than an asset.
Worth saying plainly: trafficking in counterfeit goods is illegal in the United States under the Trademark Counterfeiting Act, and US Customs can seize shipments. Personal-use buying sits on different legal ground in most states, but you should know which side of the line your seller is on.
Questions to ask before you pay
- Which reference is this actually modeled on, the 16660 or the 16600?
- What movement is inside, and is the date function native to it?
- Is the crystal flat sapphire with no cyclops?
- Can you send a straight-on photo of the helium valve at 9 o'clock?
- What is the return policy if the bezel action arrives loose?
If a seller cannot answer the first question, the rest does not matter much.