The Oyster case is one of the foundations of the reputation for excellence of Rolex watches. Invented by Rolex in 1926, it was the world’s first waterproof case for a wristwatch thanks to its patented system of screwing down the bezel, case back and winding crown against the middle case. Like the mollusc, the Rolex Oyster is robust and clamped shut.
It provides a hermetic environment that protects the high-precision Perpetual movement from water, dust, or pressure.

Rolex uses 904L stainless steel for its steel watch cases. 904L is mainly used in the high technology, aerospace and chemical industries, where maximum resistance to corrosion is essential. A superalloy, 904L is extremely resistant and highly polishable. It maintains its beauty even in the harshest environments. 904L steel also provides a perfect complement to the precious metals used by Rolex.

The screw-down winding crown and the case with screw-down back form the core of the Oyster. Created by Rolex in 1953, the Twinlock system ensures that the screw-down crown is water-resistant thanks to two sealed zones, one inside the tube of the crown, the other inside the winding crown itself. This system is used on all the watches in the Oyster collection that are guaranteed waterproof to 100 metres (330 feet).

The Cyclops lens enhances the date aperture, magnifying the date display by two and a half times for easy reading. It is one of the most distinctive Rolex features, and one of the most recognizable.

The watch case is rigorously tested to ensure it meets pressure-resistance requirements. The three-step process - a vacuum test, a compression test and a condensation test - will reveal the presence of even the smallest amount of moisture inside the case.

The Explorer II is equipped with calibre 3187, a self-winding mechanical movement entirely developed and manufactured by Rolex. In addition to the conventional hour, minute and seconds hands, it features a 24-hour hand to display a second time zone. The 3187 is fitted with a Parachrom hairspring and Paraflex shock absorbers, offering greater resistance to shocks and to extreme conditions. Like all Rolex Perpetual movements, the 3187 is a certified Swiss chronometer, a designation reserved for high-precision watches that have successfully passed the Swiss Official Chronometer Testing Institute (COSC) tests. Its architecture, in common with all Oyster watch movements, makes it singularly reliable.

The four simple words Superlative Chronometer Officially Certified on a Rolex watch dial mean that the very movement inside the timepiece has endured 15 days and nights of testing by COSC (Contrôle Officiel Suisse des Chronomètres – Swiss Official Chronometer Testing Institute), an independent not-for-profit association. To receive COSC certification as a Swiss chronometer, a watch must demonstrate extreme precision in a variety of positions and temperatures. Rolex is unique in the industry: this is the standard level of quality required of every Rolex wristwatch movement.

To increase the resistance of its movements to shocks – especially if the watch is dropped – Rolex developed Paraflex, a highly efficient shock absorber designed to protect sensitive components of the movement, notably the staff of the balance wheel. Paraflex shock absorbers increase shock resistance by up to 50 per cent.

Invented by Rolex in 1931, this ingenious mechanism harnesses the energy of natural wrist movements to provide a reliable and clean source of power for the watch movement. It consists of a half-moon- shaped oscillating weight, which pivots freely in both directions on its axle. As it rotates, the rotor continuously winds the Perpetual movement’s mainspring, ensuring a constant and stable source of energy. This enhances the watch’s precision and eliminates the need to wind it regularly. The Perpetual rotor mechanism features two distinctive red reversing wheels, which ensure efficient winding of the movement regardless of the direction in which the oscillating weight rotates.

Rolex uses 904L stainless steel for its steel watch cases. 904L is mainly used in the high technology, aerospace and chemical industries, where maximum resistance to corrosion is essential. A superalloy, 904L is extremely resistant and highly polishable. It maintains its beauty even in the harshest environments. 904L steel also provides a perfect complement to the precious metals used by Rolex.