Short answer
The replica Cartier Tank Must Black is a safe buy when the seller shows three things: correct case proportions, a clean black lacquer dial, and a slim profile that matches a quartz movement. The large Tank Must measures 33.7 x 25.5 mm, the small 29.5 x 22 mm, and both are around 6.6 mm thick. Anything much thicker means a mechanical movement was squeezed into a case designed for quartz, and it will sit wrong on the wrist.
Case size and shape
The Tank is a rectangle with softened corners, and the brancards, the vertical side bars, have to run straight and parallel. On cheap replicas they taper or bow outward. Check the caseback too: it should be flat, engraved with reference and serial, and flush with the case. Screws sit even and at the same depth. I look at the lugs next. They should be short, worked into the case, and drilled straight, because a crooked spring bar is what makes a replica perch on top of the wrist instead of draping.
Dial details
The black lacquer dial is where replicas separate. Real printing is sharp enough that the white Roman numerals read as stamped, not painted. On a weak copy the numerals look thick, the edges fuzzy, and the chemin de fer minute track wanders where it turns the corners. Study the XII and VI first. Then check the hands: blued steel swords should be polished steel, not painted blue, with a clean point and no burr on the tail. Most black dial Tank Must references are time only, so a date window is a warning sign unless the seller can name the exact reference being copied.
Crown and cabochon
The crown is a fluted steel button with a domed blue cabochon. Real synthetic spinel has depth and a slightly milky rim. The plastic or glass beads on cheap reps look flat and cloudy, and they are often glued in off center. Run a fingernail along the setting. It should feel level and smooth, with no gap between stone and bezel.
Movement and thickness
The genuine Tank Must runs on quartz, which is the reason it stays this thin. Reps that use an automatic movement usually add a millimeter or more and the caseback bulges. If a seller advertises an automatic as an upgrade, ask for a side profile photo next to calipers. That single image tells you more than any spec sheet.
Strap, buckle, and finish
Most black dial models ship on leather with a steel ardillon or folding buckle. On replicas the leather is the first thing to give the watch away, feeling stiff and glossy. A decent seller will offer an upgraded strap. Check the buckle for thickness and engraving depth; thin stamped metal with shallow text is a common shortcut. Brushed surfaces should show fine even grain, and polished bevels should catch light in a straight line rather than a smeared one.
Red flags
- Listings with stock photos only, no real images of the actual watch.
- No stated case dimensions, or numbers that do not match the size you asked for.
- Crystal that scratches within a week, which means it was never sapphire.
- Cabochons that arrive loose or fall out.
- Black coated cases with flaking at the lug edges instead of an even matte finish.
Ask for a daylight wrist shot, ask what movement is inside, and ask about returns before you pay. That conversation filters out most of the bad sellers on its own.