Short answer

A fake Rolex 16660 copies the Sea-Dweller Triple Six, built from 1978 to 1989. The real watch has a 40 mm steel case, a sapphire crystal with no magnifier over the date, a helium escape valve at 9 o'clock, and a 1,220 m (4,000 ft) depth rating. Most copies fail on the crystal, the case thickness, the rehaut, and the movement.

What the real 16660 is

Rolex brought out the reference 16660 in 1978 as the replacement for the 1665. Production ran to 1989, when the 16600 took over. Collectors call it the Triple Six.

  • Case: 40 mm, stainless steel, thicker than a Submariner of the same period.
  • Crystal: sapphire. It was the first Sea-Dweller with sapphire in place of acrylic.
  • Water resistance: 1,220 m / 4,000 ft, up from 610 m on the 1665.
  • Helium escape valve: left case flank, 9 o'clock.
  • Movement: caliber 3035, 27 jewels, 28,800 vph, quick-set date. Late examples used the caliber 3135.
  • Date: no cyclops magnifier. The crystal sits flat above the dial.

Tells on a copy

  1. Cyclops over the date. The 16660 has a flat crystal and a bare date window.
  2. Engraved ROLEX ROLEX rehaut. Rolex added that in 2005, 16 years after the 16660 ended.
  3. Case too thin. A Submariner case with a Sea-Dweller dial does not match the 16660 profile.
  4. Valve that does not turn. Real valves thread into the case and can be serviced.
  5. Movement beat rate. The genuine watch runs at 28,800 vph, 8 beats per second. Many copies run at 21,600 vph or use quartz.
  6. Dial print. Check the depth line 1220m = 4000ft, the Sea-Dweller line, and the tritium mark at 6 o'clock under a loupe.
  7. Hands and lume. Old tritium on a genuine dial ages to a warm tone. Fresh paint on a copy looks flat under UV light.

How to check one

Ask for photos of the caseback, the crown, the lugs, and the movement. Take the watch to a watchmaker who services Rolex. The movement, the case markings between the lugs, and the caseback stamp settle the question. Serial numbers do not prove a watch is real, because cases get swapped and serviced.

What is not known

Rolex does not publish production totals for the 16660. Service parts, replacement dials, and swapped bracelets are common on watches this age. A watch can be genuine and still carry a later dial or hand set. A firm answer comes from an inspection by a qualified watchmaker.