A locking pin is a small cylindrical device that you place at the end of a nut to prevent it from turning. These pins come in different sizes and lengths to fit the hole on nuts of various sizes. Depending on your application and preference, locking pins also come in different types like ball lock pins and lifting pins. These pins prevent the release of the nut until you remove the pin. Removing the pin is not difficult; all you have to do is press the top to release it from the hole. These pins are also commonly used in gyms to lock the weights before you use the weight machines.