The document discusses shafts and keys, which are basic mechanical engineering components. It defines shafts as rotating members that transmit power or motion. There are two main types of shafts: transmission shafts and machine shafts. Transmission shafts include line shafts and counter shafts. Keys are used to secure rotating elements on shafts and prevent relative motion. There are various types of keys including sunk keys, saddle keys, and splines. The document provides details on the properties, materials, and applications of shafts and the different types of keys.