The short answer: judge a fake Rolex 16600 on three things before anything else. The crystal must be flat sapphire with no date magnifier. The case must measure about 40mm across and roughly 14.8mm thick, which makes it noticeably taller than a Submariner of the same era. The helium escape valve must sit on the left case flank at 9 o'clock with correct proportions and a working crown. A replica that fails those three checks cannot be rescued by a better movement or a nicer bracelet, because the fault is in the case set itself.

What the genuine 16600 actually is

Rolex produced the Sea-Dweller 16600 from the late 1980s until around 2008, when the Deepsea took over the line. It carries a 40mm Oyster case rated to 1,220 metres, which is 4,000 feet in the older marking convention. The dial reads Sea-Dweller below centre, and the watch uses a domed sapphire crystal with no cyclops over the date. Inside sits a Rolex calibre 3135, an automatic movement with a quickset date. The bracelet is the 93160A with solid end links, a flip-lock clasp and a diver extension. Lugs are 20mm. Earlier examples came with lug holes and tritium lume; later ones dropped the holes and moved to a luminous compound that does not age the same way.

Checks that separate a good replica from a poor one

Case and crystal

Measure thickness, not just diameter. Fakes often reuse a Submariner midcase, which comes out too thin and makes the whole profile look wrong. Check the crown guards, which should be asymmetric and wrap the crown without swallowing it. The crystal should sit close to the bezel with minimal edge height and no distortion ring at the rim.

Dial, date, and hands

Print quality is the fastest tell. Look at the Sea-Dweller text weight against the depth rating, the spacing of the crown coronet above the logo, and whether the date wheel font matches the period. Hands should be the correct length, with the minute hand reaching the chapter ring and the hour hand stopping short of the markers. Lume colour must match across dial and hands.

Valve, crown, and caseback

The valve is the part most replicas get wrong. It should be flush, threaded, and sized in proportion to the case band. A valve that is glued in place or visibly undersized is a hard fail. The caseback engraving should be crisp with correct letter spacing around the ring.

Movement and bracelet

Ask what powers it and how the date changes. A clone of the 3135 with a proper quickset and smooth crown action is the better tier. A generic ETA-style automatic is common and workable but usually shows a rougher winding feel and a slower beat. On the bracelet, check for solid end links that sit flush against the lugs with no rattle, and a clasp that locks without play.

Parameter bands worth insisting on

• Case diameter: 39.8mm to 40.2mm across, excluding the crown.
• Case thickness: roughly 14.6mm to 15.0mm, thicker than a Submariner.
• Lug width: 20mm, with end links that fill the gap without a visible seam.
• Crystal: flat domed sapphire, no magnifier, no blue tint at the edge.
• Bezel: 60-click or 120-click action with firm detents and no back play.
• Crown: threaded, screw-down, with at least four full turns to seat.

Pitfalls that cost the most

• A cyclops over the date. The genuine 16600 does not have one, so any replica that does is wrong at a glance.
• Submariner case geometry reused as a Sea-Dweller. The thickness and the valve are the giveaway.
• Photographs that hide the left case flank. Always ask for a straight-on shot of the 9 o'clock side.
• Dealers who will not show a movement photo or a timed rate reading.
• Markers described as aged tritium when the lume colour is uniform and fresh.

Legal and practical reality

Counterfeit watches are illegal to import into the United States. Goods bearing a copied trademark can be seized at the border, and trafficking in counterfeits carries federal criminal exposure. That means the practical risks are not only accuracy and build quality but also forfeiture, with no recourse if a shipment is stopped. Factor that in before spending, and treat any claim of guaranteed delivery as a red flag rather than a feature.

FAQ

Is the 16600 the same size as a Submariner?

No. Diameter is close at 40mm, but the Sea-Dweller case is thicker and carries the helium escape valve on the left flank.

Should a 16600 replica have a date magnifier?

No. The genuine watch has a flat crystal with no cyclops. A magnifier is one of the clearest signs of a mismatched build.

Which movement should I look for?

A 3135 clone with quickset date is the closer match. A generic Swiss or Asian automatic can work but usually feels coarser when winding and setting.

Does lume colour matter that much?

Yes. Mismatched lume between dial and hands is visible in daylight and under UV, and it is difficult to correct after purchase.

What single photo should I request?

A sharp side profile of the left case flank showing the valve, plus a straight-on dial shot at close range.