Description: Cotter pin or split pin is for locking or securing an object. It is used by inserting through a clevis pin's one end. This metal fastener comes with two tines. During installation, these tines can be bent. By doing so, it prevents a nut from moving and coming loose. There are varying styles for split cotter pins. Each one serves a specific purpose or application. To find the correct cotter pin, you have to consider its length and diameter. To get the length, measure from its eye until the shorter tine. For the diameter, measure the short and long tines together. The eye or the rounded portion should be larger than the hole you're going to insert the cotter pin through.