Split pins, also known as cotter pins, are small, U-shaped fasteners used to secure components and prevent them from loosening or falling off. Made from metal, they have two prongs that are bent or "split" to lock them in place once inserted through a hole in a bolt or axle. In motorcycles, split pins are commonly used in various applications, such as securing cotter bolts, attaching linkages, and holding in place key components like brake calipers and suspension parts. They provide a simple, reliable means of securing fasteners and ensuring the integrity of critical components.