Split pins, also known as cotter pins or split cotter pins, are a type of metal fastener used in engineering applications to hold nuts and other components in position.
Split pins are made from a heavy wire and are semi-circular in section. Each pin has two legs that are bent into position once the pin has been inserted – usually through a small hole in a shaft or a bolt.
To insert a split pin, offer the legs of the pin up to the hole in the component and tap the pin through until the head of the split pins meets resistance. Then grasp the legs of the pin and bend them outwards to lock the pin and component in position.
Metric is the most common thread type in production today. Usually specified as M then a number x another number. This signifies the thread diameter and the length of the fastener.
For example M4 x 30 means that the major thread diameter (the external distance across the outside of the thread) is 4mm and the length is 30mm. Length is usually measured from the underside of the fastener head.