This lecture covers the mechanical behavior of solids, including the deformation law characterized by tensile testing, the elastic-plastic behavior of common materials, and the frictional contact between solids defined by Coulomb's laws. It also discusses assembly functions, ISO tolerance system, and the principles of bolted assemblies. The instructor explains the concept of mechanisms, the components of mechanical systems, and the various types of mechanical linkages. Additionally, it delves into the principles of threaded fasteners, focusing on the functions and characteristics of threads, standardized metric threads, and the design and manufacturing of threads.