A cottar pin, also called a split pin, is a soft metal fastener consisting of a ring at one end and two straight prongs. The prongs are inserted through a hole that is smaller than the ring. The ring holds the pin at one end, and the prongs must be bent to secure the other end. Cotter pins secure nuts on bolts, fasten drawer pulls on drawer boxes and hold some low force mechanical parts together.
Select a cottar pin whose prongs are adequately long enough to split at the far side of the fastening hole.
Push the cottar pin completely through the hole. Grip the prongs with needle nose pliers, if necessary, to pull them through holes in tight spaces. Split pin holes are found in bolts that hold castle nuts, drawer box faces and sleeve connectors adjoining mechanical parts.
Split the prongs of the cottar pin apart and, with your fingers or the pliers, bend them outward in opposite directions. Wrap the individual prongs around the adjacent parts. Bend one prong around the bolt end and the other around the nut for securing castle nuts. Bend both prongs around opposite sides of connector sleeves on machine parts. Use needle nose pliers to bend prongs in spaces that can't be reached with fingers.
Secure a drawer pull with a cottar pin. Open the prongs of the pin and slide a drawer pull into the ring. Close the prongs together and push them through the hole in the drawer face. Separate the prongs inside the drawer box and slip them into small holes drilled to receive them. Hammer the separated prongs flat against the inside of the drawer box.
A tool called a cottar pin puller is available for removing these fasteners from tight places. It has a handle like a screwdriver, and a straight post that angles at an L-shape and narrows to a pointed tip. Grab the ring of a split pin with the tip and pull upward, or twist the tool, to remove a fastener.