Plastics are now rapidly displacing conventional materials in numerous engineering applications in mass productions. The emerging need to produce larger and more complex forms of plastics and their composites has increased the need for joining, in particular, the thermoplastics. Thread fasteners have found widespread use in many systems and structures. Although frequently overlooked they represent a complex and often critical design element. Fastened assemblies are often subjected to dynamic environments including vibration, shock, and/or thermal cycling. Such conditions can lead to fastener loosening and can result in increased maintenance and failure.