The genuine Cartier Tank Must does not come in a 31mm size. Cartier lists two sizes: Large (33.7mm x 25.5mm) and Small (29.5mm x 22mm). A 31mm label on a replica is not a Cartier reference. Measure the case at 3 and 9 o'clock. That number is the case width.
Genuine Cartier Tank Must Sizes
Cartier publishes two Tank Must sizes. The Large model measures 33.7mm x 25.5mm. The Small model measures 29.5mm x 22mm. Both cases are steel. Both have a thickness of 6.6mm. Both use quartz movements. The crystal is sapphire. Water resistance is 30 meters (3 bar). The dial has Roman numerals. The crown has a blue spinel cabochon.
What a 31mm Replica Usually Means
A 31mm listing often uses the case width at the widest point. That point sits at the lugs. A 31mm case may copy the Tank Solo small (31mm x 24.4mm). The Tank Solo is a different model. The Tank Must replaced the Tank Solo in 2021. The Tank Must has a different dial and crown. Check the model name on the dial. The Tank Must dial says "Cartier" in italic. The Tank Solo dial says "Cartier" in a different font.
Movement and Case Checks
- Movement: Genuine uses quartz. Replicas use quartz or automatic. A quartz replica ticks once per second. An automatic moves 6 to 8 times per second.
- Case thickness: Genuine is 6.6mm. A thick case often measures 8mm or more.
- Crown: Genuine has a blue spinel cabochon. Replicas use glass or plastic. Check color and light reflection.
- Dial: Genuine prints "Cartier" in italic. Check font weight and spacing. The Roman numerals must line up with the chapter ring.
Strap and Buckle
Genuine straps use alligator or calf leather. Replicas use synthetic leather. The buckle has the Cartier logo. Check engraving depth. Low-cost replicas have shallow engraving. High-cost replicas have deeper engraving.
Weight and Finish
Genuine steel case weighs about 30 grams without strap. Replicas often weigh less. Polished surfaces show sharp edges on low-cost replicas. Genuine edges are smooth. Check the lugs and the case back.
What to Ask a Seller
- Movement type and maker.
- Case width in millimeters at 3 o'clock.
- Case thickness in millimeters.
- Crystal material (sapphire or mineral glass).
- Crown cabochon material.
If a seller cannot give these numbers, the watch is unknown. No data means no answer.