Cryptex
A mechanical lock with rings of letters, best known from Dan Brown's The Da Vinci Code (2003).
A cryptex is a cylinder with rotating rings of letters; the right word in the right order opens it. It is a combination lock with letters instead of digits, not a cryptographic algorithm, and its security rests entirely on nobody knowing the word. In the novel it serves as a container for a message and as a prop for a chase.
The novel made the cryptex famous, and replicas have been sold as puzzle boxes ever since.