Keyed cylinders are locking mechanisms commonly used in doors and other security applications. They consist of a cylindrical body that houses a series of pins, which align when the correct key is inserted. This alignment allows the cylinder to turn and unlock the door, providing access. These cylinders come in various types, including single-cylinder and double-cylinder designs. Single-cylinder models use a key on one side and a thumb turn on the other, while double-cylinder models require a key on both sides. Keyed cylinders are widely used in residential and commercial settings for their reliability and security features.