Cotter Pin (Split Pin)

http://demonstrations.wolfram.com/CotterPinSplitPin/ The Wolfram Demonstrations Project contains thousands of free interactive visualizations, with new entries added daily. Cotter pins are generally used to prevent a machine part from moving in the axial direction. The pin is inserted in a hole across a cylinder and its protruding ends are bent to stop it from falling out. The cross section of the cotter pin is a semicircle. Contributed by: Sandor Kabai