A split pin, also known as a cotter pin or cotter key,it is a metal fastener with two tines that are bent during installation, similar to a staple or rivet. Typically made of thick wire with a half-circular cross section, split pins come in multiple sizes and types.
A split pin has its flat inner surfaces touching for most of its length so that it appears to be a split cylinder Split pins are typically made of soft metal, making them easy to install and remove. Common materials include mild steel, brass, bronze, stainless steel, and aluminium. The most common type of split pin is the extended with a square cut, split pins are properly installed by striking the head with a hammer to secure the pin.
This forces the shorter tine forward, spreading the pin. Split pins are frequently used to secure other fasteners, e.g. clevis pins, as well as being used in combination with hardboard discs as a traditional joining technique for teddy bears.