Short answer
A fake Rolex 16660 is a counterfeit of the Sea-Dweller that Rolex built from 1978 to 1989, the reference collectors call the "Triple Six." It was the first Sea-Dweller with a sapphire crystal, the first with the caliber 3035, and it is rated to 1,220 m (4,000 ft). Copies exist in every price band, from $70 market-stall junk to $600 "super clone" builds, and almost none of them get the case profile right. The 16660 is thicker than a Submariner, has a helium escape valve at 9 o'clock that genuinely functions on the real watch, and prints "4000 ft = 1220 m" on the dial. Those three details are where most replicas fall apart first.
What the real 16660 is
- Production: 1978 to 1989, replaced by the 16600
- Case: 40 mm across, roughly 15 mm thick, 20 mm lugs
- Movement: caliber 3035, then the 3135 in later examples
- Helium escape valve on the left side of the case at 9 o'clock
- Flat sapphire crystal, no cyclops over the date
- Matte black dial with tritium plots, white gold surrounds on later runs
- Water resistance: 1,220 m / 4,000 ft
The valve matters. The 1665 that came before it had a similar fitting, but the 16660 is the reference that took the line from plexi and 610 m into the sapphire era. It is also the watch that pushed the Sea-Dweller case noticeably deeper than a Submariner, which is the whole reason it is a hard watch to fake convincingly.
Why the 16660 is harder to copy than a Submariner
A Submariner clone can hide behind a familiar silhouette. The 16660 cannot. Its case is a slab compared to a 5513 or a 1680, the caseback is domed and engraved, and the valve sits proud of the caseband on the left. A factory that stamps a Submariner midcase and bolts a fake valve onto it produces something that looks wrong from two feet away in profile, even if the dial and bezel are convincing.
Then there is the dial. Genuine 16660 dials carry "ROLEX OYSTER PERPETUAL" over "Sea-Dweller" and the depth rating below, with a date at 3. Most copies get the font weight and the spacing of the depth line wrong, and many print the rating as 2000 ft = 610 m, which belongs to the earlier 1665.
What I check on a replica 16660
- Helium valve: on the real watch it unscrews and seals. On most fakes it is a fixed stud, or it unscrews and does nothing. Compare the diameter and how far it protrudes.
- Case thickness and caseback: a correct build runs close to 15 mm thick with a domed back and proper engraving. Thin cases and flat backs are the giveaway.
- Dial text: check the depth rating, the serif shapes, and whether the tritium plots sit level with the minute track.
- Bezel insert: font thickness, the position of the pip, and whether the insert sits flush or stands proud of the bezel ring.
- Crown guards: the 16660 guards are broad and asymmetrical. Copies tend to be either shaved thin or left as blunt blocks.
- Crystal: flat sapphire, no cyclops, and the date should not be magnified. A magnifier on a Sea-Dweller is a clear tell.
- Bracelet: solid end links that sit tight against the lugs, correct Oyster clasp stamping, and no rattle at the pivot points.
Movements and price bands
Below $150 you are usually looking at a low-grade automatic or quartz with a decorated rotor. From $250 to $450 the market moves to Asian 2824 and 2836 clones, which keep decent time but sound and feel nothing like a 3035. Above that, builders use clone 3135 movements with date quickset and a free-sprung balance. Those are the ones people mean when they say super clone, and they are also the ones that cost enough that servicing becomes an awkward question, since no independent watchmaker wants to open a counterfeit.
Reality check
None of this makes a copy a 16660. Counterfeits infringe on Rolex trademarks, selling them is illegal in the US and most of Europe, and a replica has no resale market worth counting on. Genuine 16660 prices have climbed for years, which is exactly why the fakes got better. If you are buying the real thing, a service record and a caseback photo are worth more than any dial detail.