Rolex Oyster Case (photo: Rolex)

The Oyster was the first waterproof wristwatch case that utilized Rolex's patented system of screwing the bezel, case back and winding crown into the middle case. It was tested by famed swimmer Mercedes Gleitze, who swam across the English Channel with a Rolex Oyster provided to her by Hans Wilsdorf in 1927.

All of the Rolex Oyster Perpetual models currently on the market are water resistant up to at least 100 meters due to the hermetic construction of the Oyster case. Today's Oyster case is made of a middle case that is stamped out of a solid block of metal (904l steel, 18 karat gold or platinum), a screw-down fluted case back and friction fitted crystal and bezel. Either a Twinlock or Triplock winding crown is also screwed into the Oyster case for watertight security.

All Oyster cases are made by Rolex in-house and undergo rigorous testing, including immersion underwater with high pressure to assure quality control. Although it may feel redundant to add the word 'Oyster' to every model name, the shape of the Oyster case is one of the easiest ways to identify a Rolex.

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