The screw down winding crown was an important component of Rolex's first waterproof Oyster case design in 1927. Due to the fact that the winding crown interacts directly with the movement inside the case to perform essential functions of the watch, it is imperative that it creates a tight seal with the case to keep dust and water out. 

Rolex Triplock Winding Crown (photo: Rolex)

Rolex wristwatches are equipped with either a Twinlock or Triplock winding crown, depending on the model's depth rating. The Twinlock came first, introduced in 1953. Identifiable by two dots below the crown, the Twinlock winding crown has two sealed zones, one inside the tube and one inside the crown, to keep water out up to a depth of 100 meters.

The Triplock winding crown was introduced in 1970 and contains a third sealed zone inside the crown that increases water resistance to depths of up to 3,900 meters on the Rolex Deepsea model. The Submariner and Sea-Dweller models are also equipped with Triplock winding crowns.

While the winding crown may not be a deciding factor when purchasing a Rolex, it serves an important purpose in the hermetic seal of the Oyster case that the watchmaker has been perfecting for almost a century.

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