No Cartier Tank Must measures 31mm. Cartier lists the Must in Small (29.5 x 22mm) and Large (33.7 x 25.5mm), and that has been the lineup since the steel relaunch in 2021. A 31mm tag in a listing is a seller's number, not the house's. Most of the time it means the case was measured across the crown, or the seller is describing a mid-size replica case that sits between the two genuine sizes. That matters more than it sounds, because a spec sheet that starts with a wrong dimension is often a spec sheet that got other things wrong too.
What the 31mm label tells you before you look at the watch
Size listings on replica sites are marketing, not measurement. Sellers round up because a bigger number reads as more watch for the money. So treat 31mm as a prompt to ask one question: does the seller give case length and width separately, or just one figure? A serious seller lists both, plus thickness and lug width. If you only get a single number, expect the same vagueness on movement, crystal, and finishing.
Ask for a photo of the watch next to a ruler or a caliper. It takes the seller half a minute and it settles the size question.
Dial details that give a replica away
Two things matter most on the Tank Must dial: the hidden signature and the hands.
- The VII: Cartier works the word CARTIER into the strokes of the Roman numeral VII at 7 o'clock. On a genuine dial you catch it when you tilt the watch into the light, and it fades when you look straight on. Replicas either omit it or print it so heavy that it reads from across the room. Both are wrong.
- No seconds hand: The Tank Must is a quartz watch with two hands. If the listing shows a sweeping center seconds hand or a small seconds subdial, the dial was not copied from a Must.
- Numeral weight: The printed Roman numerals should be crisp with clean serifs, and the rail track around the minute ring should be unbroken. Blurry edges show up fast in macro photos.
- Blued sword hands: They should be a deep steel blue, not painted navy, and the tips should reach into the minute track without touching it.
Case, crown, and the blue cabochon
The Tank Must case is steel and thin, around 6.6mm on the quartz versions. Look at how light breaks across the brancards, the vertical bars on either side of the dial. Cartier mixes satin and polished surfaces here, so you should see a shift between the flat case sides and the edges. A case that is polished everywhere looks like a different watch under a desk lamp.
The crown carries a blue cabochon, a synthetic spinel on the steel models. It should sit as a smooth dome with no seam where it meets the metal, no glue line, no flat top. This is one of the easiest places to spot a cheap build, because the stone is set by hand and hand-setting costs money.
Caseback, engraving, and serials
Flip it over. The engraving should be cut into the metal with sharp edges. Laser-etched text on a fake tends to look soft or frosted, and it catches light in a hazy way instead of throwing shadows. Check the placement of the brand script, the reference and serial numbers, the water resistance rating, and the Swiss Made line. Then check that the numbers match what the seller showed you in the photos. Swapped casebacks are common in the replica market.
Strap, bracelet, and buckle
Leather versions of the Must use a strap that pops off without tools, thanks to Cartier's quick-release system. If a seller claims a leather-strapped Must and the strap is sewn in, the case is likely an older or cheaper copy. On the buckle, the engraving should be as clean as the caseback. Bracelet versions are harder to fake well, so look at the links and how the clasp closes. A rattling bracelet on a watch this thin is a bad sign.
Before you pay, run this list
- Ask for length, width, and thickness as separate figures.
- Ask for a macro shot of the VII numeral.
- Confirm two hands, no seconds.
- Ask what movement is inside, and whether it is quartz.
- Request close photos of the crown cabochon and the caseback engraving.
- Check the return policy, since none of this helps if you cannot send it back.
A replica Tank Must can be a good watch. The line is thin and the movement is quartz, so the gap between a careful copy and the real thing comes down to finishing, not mechanics. Know the real dimensions, know the dial, and ask for photos that prove it. That is most of the work.