What is the name of the pin used to secure the end of the shackle bolt after the locking nut is installed?

The pin used to secure the end of the shackle bolt after the locking nut is installed is called a cotter pin. A cotter pin is a type of fastener that is commonly used to prevent the loosening of components in mechanisms, such as those found in roller coasters and amusement rides. When a locking nut is tightened on a shackle bolt, the cotter pin is inserted through the bolt's hole to ensure that the nut remains secure and does not loosen over time due to vibration or forces during operation. This adds an essential layer of safety, helping to maintain the integrity of the assembly under stress.

Other potential options, such as a security pin or safety pin, do not describe the specific component used in this application, which further highlights the distinct purpose of the cotter pin in this context. The term "locking pin" also does not apply, as it refers to components used to immobilize parts or mechanisms rather than secure a shackle bolt in place. Understanding the function and proper terminology of fasteners like the cotter pin is crucial for maintaining safety and effectiveness in mechanical systems.