This document discusses cotter and knuckle joints. It provides diagrams of a cut section of a socket and spigot joint, showing how the cylindrical spigot fits inside the socket. It also contains diagrams of a knuckle joint, which allows rotation between two connecting components about an axis perpendicular to their common plane. The document was authored by Hareesha N G of the Department of Aeronautical Engineering at Dayananda Sagar College of Engineering in Bangalore, India.