The Short Answer
A fake Rolex 16660 is a counterfeit of the Sea-Dweller "Triple Six," the reference Rolex produced from 1978 into the late 1980s. It gets copied for a simple reason: the watch is old enough to have a matte dial and tritium lume that are easy to imitate, valuable enough that a good copy pays for itself, and rare enough that most buyers never handle a genuine one. Spotting one comes down to five things: case and crystal height, the helium escape valve at 9 o'clock, the dial and its lume, the crown, and the movement behind the case back.
What the Genuine 16660 Actually Is
- 40mm Oyster case with a thicker mid-case and case back than a Submariner of the same period.
- Flat sapphire crystal, a first for the Sea-Dweller line. No cyclops magnifier over the date.
- Helium escape valve on the left side of the case at 9 o'clock, one-way and functional.
- Depth rating of 4,000 ft / 1,220 m printed on the dial.
- Caliber 3035 (28,800 vph, quickset date), later swapped to the 3135 near the end of production.
- Matte black dial with painted tritium markers on early examples, glossy dial with white gold surrounds on later ones.
- Triplock crown, roughly 7mm across, larger than the Twinlock used on Submariners.
- Serial between the lugs at 12 o'clock and the reference between the lugs at 6 o'clock. No rehaut engraving of any kind.
Where Replicas Give Themselves Away
Case and crystal height
Replica cases tend to be too thin through the mid-case or too tall at the crystal. A real 16660 has a sapphire that sits almost flush with the bezel insert, with a hard edge and no anti-reflective coating. Copies usually show a domed or cloudy crystal that catches light in a way the original never does.
The helium escape valve
This is the fastest check. On a fake, the valve is often a decorative plug glued or pressed into the case. It sits proud of the case band, or sits on the wrong plane. On the real thing it threads into the case, sits close to flush, and has crisp machining. If the seller will not let you look closely at 9 o'clock, walk.
Dial, lume, and date
Genuine tritium does not glow anymore. It has gone cream or pumpkin over decades. A replica dial usually carries Super-LumiNova or painted amber that either glows under a light or looks flat and uniform. Check the spacing of "SEA-DWELLER" and the 4000 ft line, the date font, and the position of the date window. Replica date wheels are often the wrong thickness or use a modern Rolex font that did not exist in 1980.
Movement and crown
Most fakes run an ETA clone or a generic automatic with a date, not a 3035. That means the winding feel, the crown position count, and the beat rate are all wrong. The crown itself is often a standard Submariner-style piece instead of the larger Triplock, and the crown guards are usually too fat or too soft.
Case back and bracelet
Real 16660 case backs are stamped inside, not laser etched with modern text. Bracelet end links should fit the lugs with no gap, and the clasp stamping should match the era. Shiny, freshly polished bracelets on a watch sold as untouched are a warning sign.
Franken Watches Are the Harder Problem
A straight fake is easy to catch. A franken 16660 is not. These are built from a genuine case or case back paired with a reprinted dial, an aftermarket bezel insert, and a service movement. Each part passes on its own. What exposes them is inconsistency: a tritium dial with a service handset, a case with sharp lugs under a worn bracelet, or a serial range that does not line up with the dial style. If you are buying at this price point, pay for an independent check from someone who has handled a 16660 in person.
Price Reality
Genuine 16660 examples trade in the five-figure range depending on dial type and condition. That gap is exactly why replicas exist. If a listing is priced far below market and the photos are soft, the watch is either a fake, a franken, or a genuine piece with a serious problem.