Retaining rings, also known as snap rings, are circular fasteners used to secure components on shafts or in housings. They fit into a groove and prevent parts from moving axially, ensuring that assemblies remain intact during operation. These rings are commonly made from materials like steel or stainless steel for durability. There are two main types of retaining rings: internal and external. Internal retaining rings fit inside a bore, while external retaining rings fit around the outside of a shaft. Both types are essential in various applications, including automotive, aerospace, and machinery, to maintain the integrity of mechanical systems.