The short answer
A genuine Cartier Tank Must in steel is a quartz watch that starts in the low four figures new. If a listing asks a few hundred dollars and calls it a Tank Must, it is a replica. Most copies get the silhouette roughly right and then fall apart in three places: the crown, the dial printing, and the caseback.
What the Tank Must actually is
Cartier brought the Must name back in 2021, a nod to the Les Must de Cartier line from the 1970s that put entry-level Cartier on a lot of wrists. The modern steel version has a rectangular case, a quartz movement, a sunray-finished dial, and two sizes: Large at roughly 33.7 by 25.5 mm and Small at roughly 29.5 by 22 mm. There is also a SolarBeat model with a photovoltaic movement and a strap partly made from apple waste. Keep that in mind, because the design is plain by intent. There is nowhere for a faker to hide a mistake.
Where replicas slip
Case and proportions
The vertical side bars, called brancards, should be flat and tight, with a crisp line where they meet the bezel. Copies tend to look soft at the edges, with lugs that are a touch too thick and a case that sits slightly tall on the wrist. Weight is a poor test on its own, since steel is steel.
Dial and printing
Look at the word Cartier in the upper dial and Swiss Made at 6 o'clock. On the real thing the letterforms are thin, even, and sharp under magnification. Fakes show jagged serifs, spacing that drifts, and Roman numerals with heavy strokes. The sunray finish should shift evenly as you tilt the watch. Cheap dials look flat or cloudy. One clean giveaway: the Tank Must is a two-hand watch. A seconds hand means it is not one.
Crown and cabochon
The crown carries a faceted blue spinel cabochon, set straight and flush. Fakes use resin or glass that reads dull, or set the stone at an angle. The crown itself should be polished with a clean beaded profile.
Caseback, papers, and serial
Engravings on the caseback should be sharp and consistent, not stamped and shallow. The case serial should match the certificate and the reference on the paperwork. Ask for a clear photo of all three together in one frame. Sellers of copies rarely have that.
Strap and clasp
Factory leather is firm and evenly stitched, and the pin buckle carries crisp engraving. Aftermarket straps are normal on a used watch, but a mismatched strap plus blurry photos plus a low price is a pattern.
How to buy with confidence
- Buy from Cartier, an authorized dealer, or a reseller with a written authenticity guarantee and a return window.
- Ask for the serial, the card, and the original invoice in one photo.
- Have any used purchase opened by an independent watchmaker before the return window closes.
- Compare seller photos against Cartier's own product images at the same scale, side by side.
The legal side
Counterfeit watches are not a gray market. Importing them into the United States is grounds for seizure and civil penalties, and selling them exposes a seller to trademark liability. That is the practical reason a genuine Tank Must holds value and a copy does not.