The short answer: a fake Cartier Tank Must small is easy to find and hard to judge from photos, because the real watch runs on quartz as well. There is no rotor, no decorated bridges, no balance wheel to inspect, so the usual replica test does not apply here. What separates a convincing fake from an obvious one is almost entirely exterior: case proportions, the crown cabochon, dial printing, hand shape, bracelet fit, and how the caseback is engraved. Get those right and a $150 replica looks fine across a dinner table. Get them wrong and anyone who has handled the real thing will spot it in about three seconds.

What the real Tank Must small actually is

Cartier relaunched the Tank Must line in 2021 as a steel entry point into the Tank family. The small version measures about 29.5 mm by 22 mm, with a thickness close to 6.6 mm. It is a quartz watch rated to roughly 30 m of water resistance, with a sunray dial, blued sword hands, a synthetic blue spinel set in the crown, and a solid caseback. Retail sits around $3,000 and up, depending on whether you take the leather strap or the steel bracelet.

Those numbers are the measuring stick. If a listing describes a "small" Tank Must at 31 mm wide, or with a 7.5 mm thick case, it is not copying the watch that actually exists.

Where fakes give themselves away

Case proportions and profile

The Tank case is not a flat rectangle. The brancards, the vertical bars running down each side, carry a slight curve, and the lugs taper into the case rather than sitting on top like separate blocks. Replicas tend to make the case a touch too thick and the brancards too flat, which reads as a slab on the wrist. Hold a photo sideways against the spec sheet and the difference shows.

The dial, the printing, and the VII

Start with the word CARTIER under 12. Genuine printing is crisp, faintly raised, with clean serifs and even spacing. Fakes often use a heavier or thinner weight, or lettering that softens at the edges. The Roman numerals should be sharp, with no bleed into the rail track. Then check the VII at 7 o'clock, where the word Cartier hides inside the numeral as a secret signature. Plenty of fakes skip it completely, or print it so large it stops being secret.

The crown and the cabochon

The blue stone in the crown is the single most common tell. Real ones use a synthetic spinel with facets and depth, set so it sits nearly flush against the crown. Replica cabochons are often plastic, too bright, too round, or standing too proud of the metal.

Hands

Blued steel sword hands should read as deep and almost black-blue, with a fine polish across the surface. Fakes commonly use painted hands that flash a brighter blue under direct light, and the hands run a half millimeter short of the minute track.

The caseback and engraving

Engraving on the genuine watch is shallow, even, and precise. On fakes it is usually cut deeper, with uneven letter spacing and a model number that does not match the case size. Water resistance markings are frequently wrong too.

Bracelet and strap fit

On the steel version, the gaps between links should be uniform and the clasp should close with a soft, solid click. Fakes show wide, uneven gaps and sharp edges where the links were finished. If it arrives on leather, the strap should be stitched evenly and sit flush against the lugs without a visible gap.

Why the movement tells you nothing

The genuine Tank Must small uses a Swiss high autonomy quartz caliber with a battery life quoted around eight years. It ticks once per second, exactly like the cheap quartz inside a replica. A smooth sweep is not proof of authenticity, and a ticking second hand is not proof of a fake. You can open the back and read the marking, but that tells you what the case is stamped with, not what the watch is.

What replica pricing actually buys

• Under about $60: unbranded movement, low grade steel, wrong dial print, plastic cabochon. Obvious in person.
• Roughly $100 to $200: the practical middle. Correct dimensions, decent dial printing, steel case, believable cabochon. This is where most buyers land.
• Above $250: small gains in bracelet finishing and packaging. Diminishing returns.

One spec worth checking: the real watch has a sapphire crystal. Cheaper fakes use mineral glass or acrylic, which scratches faster and reflects light differently.

Vintage Must de Cartier is a different watch

If a listing says Must de Cartier and shows a gold plated case with a lacquered dial, that is the 1970s to 2000s line, not the modern Tank Must. Those vintage pieces are common and genuinely collectible, and they are also widely counterfeited. Judge them on plating wear, dial finish, and vermeil hallmarks, not on the checklist above.

Legal and practical reality in the US

Selling or importing counterfeit goods is illegal, and US Customs can seize shipments of fakes. Buying one for personal wear is a different legal question, but the practical downsides are the same either way: no warranty, no service from Cartier, no resale value, and repair shops that may refuse to touch it. If you want the look on a budget, that tradeoff is easy to accept. If you want a watch that holds value, a replica will not get you there.