A cotter pin secures two items with the use of a common hole. Place the cotter pin in the hole, the bulbous head will stop the pin from moving all the way through. Then bend the open tips to secure them in place. Depending on the application, various sizes and finishes are available. The bulbous end prevents the pin from being pulled through the hole so it is important to select a pin that has a diameter measurement larger than the hole diameter in the fastener you are working with. A split cotter pin is widely used as a replacement and fastening part for machinery, workshop, electrical equipment, car garage, truck, lawn mower, tractors, small engines, etc.