Short answer: Rolex never produced a Sea-Dweller 16666. The number is a typo or a seller invention, and the watch it stands in for is either the 16660 (the "Triple Six" from 1978) or the 16600 (the long-run model sold into the 2000s). That means the best copy is the one that matches one of those two real watches instead of a fictional reference. Judge any candidate on four criteria: case profile, dial text, bezel insert, and bracelet fit. Seller talk about "1:1" or "Swiss grade" tells you nothing.
What the 16666 listing is actually pointing at
Rolex reference numbers follow a pattern, and 16666 breaks it. The Sea-Dweller line uses 1665, 16660, 16600, 16610 and then the later 116600 and 126600. A search for 16666 almost always lands on a page selling a 16660 style build, sometimes a 16600, and sometimes a generic 40 mm dive watch with the wrong dial text. Ask the seller which real reference the build follows. If they cannot answer, the build was not made against a real watch.
Specs a Sea-Dweller build has to match
- Case width of 40 mm and thickness near 15 mm. The Sea-Dweller is a thick watch because of the deeper case back and valve.
- Flat sapphire crystal with no cyclops over the date. This is the single easiest tell at arm's length.
- Helium escape valve on the left side of the case at 9 o'clock, sitting flush.
- Dial text reading Sea-Dweller above 4000ft = 1220m, with no Submariner line.
- Oyster bracelet with a Fliplock clasp and a diver extension that folds out.
- Black bezel insert with a fully graduated 60 minute scale.
Option 1: the 16660 style build
The 16660 arrived in 1978 with a sapphire crystal, a 1220 m rating, and the helium valve that defines the model. Builds that copy it use a slightly thicker case and an earlier style dial.
- Pros: the case shape reads closer to the original tool watch look, and early dial layouts are simple to reproduce because there is less printing.
- Cons: fewer sellers stock this version, and crown guard shape is often wrong because the original has a distinct blocky profile.
- Best for: a buyer who wants the older, plainer look and does not care about bracelet end link perfection.
Option 2: the 16600 style build
The 16600 ran from the late 1980s into the 2000s and is the version most people picture when they hear Sea-Dweller. It uses a thinner case profile than the 16660 and a dial with cleaner text spacing.
- Pros: the most widely produced copy, so parts and bracelets are easy to source, and the date window and bezel insert are well understood by most factories.
- Cons: because it is common, the market is full of low effort builds with painted bezel numbers and shallow dial printing.
- Best for: a wearer who wants the recognizable version and can inspect the dial before paying.
What separates a careful build from a careless one
- Dial printing under magnification. Genuine text has crisp edges and consistent letter height across the whole line.
- Bezel insert numbers. Paint should sit level with the insert surface, not raised and glossy.
- End link fit. A gap at the lugs or a bracelet that rattles is the fastest sign of a rushed assembly.
- Crown action. The winding should feel smooth with no grinding, and the date should flip cleanly at midnight.
- Case back engraving. Depth of the stamp matters more than the wording itself.
What you give up with any copy
- No Rolex warranty and no service from an authorized center. Any repair goes to a local watchmaker.
- No resale market. A copy sells for a fraction of what you paid, and often not at all.
- Movement differences. Originals used Rolex calibers 3035 and later 3135, and no copy reproduces that architecture.
- Legal exposure. Selling a copy as genuine is trademark infringement in the United States, and importing counterfeits can lead to seizure.
Who should pick which
If you want a thick, older style dive watch and you accept that it is a costume piece, the 16660 build is the better match. If you want the version most people recognize and you plan to wear it daily, the 16600 build is easier to live with and easier to find. If you want a watch with real service support, water resistance you can trust, and value you can recover, buy a genuine Seiko, Citizen, or microbrand diver instead. A copy is jewelry that happens to tell time, and it should be priced and treated that way.
Bottom line
Searching for a replica Rolex Sea-Dweller 16666 means the listing already has one error in it. Correct the reference to 16660 or 16600, match the four criteria above, and inspect photos of the crystal, bezel, and end links before you commit. The number on the page is a marketing accident. The specs on the case are what you actually buy.