The Cartier Tank Obus (Reference 1630) is a highly collectible vintage dress watch from the 1990s. Known for its unique geometry, it breaks from the traditional rectangular Tank silhouette by offering a perfectly square case paired with prominent, bullet-shaped lugs ("obus" translates to shell or bullet in French).

• Case Dimensions: 24.5 mm x 24.5 mm square case (31 mm lug-to-lug length including the bullet horns), with an ultra-thin profile of around 5 mm. 

• Case Material: Solid 18k Yellow Gold. 

• Dial: Silvered grained / creamy silver finish decorated with crisp, painted black Roman numeral indices and an inner railroad minute track. It features the secret "Cartier" signature hidden within the "V" of the VII numeral. 

• Hands: Signature blued steel Breguet-style hands (sometimes found with sword hands depending on the exact series).

• Movement: Reliable Cartier Caliber 157 quartz movement.

• Crown: Circular-grained crown finished with a signature blue sapphire cabochon.