Cotter Pins - simple fasteners

Of all the fasteners out there, cotter pins are among the most basic of all. They are simply a short piece of wire formed into the shape of a pin. There is a closed rounded loop on one end which transitions into two straight pieces that are closed together to form a straight pin shape.

There are two common applications for these pins. They hold loose fitting linkages together, and they keep nuts from backing off of a bolt or stud. In either case, use of these fasteners requires that a hole be drilled through one part.

The part of the assembly that usually has a hole in it will be the part that's being asked to hold the other part in place.

To use this fastener, the straight is inserted into the hole first. The looped end prevents the pin from slipping into the hole. Various sizes of pins are made to accommodate diameters and depths of holes.

Although easily removed, cotter pins are designed for long term use - not for frequent removal and re-installation. If the pin needs to be removed with any regularity, a hitch pin is a better choice.

After installing a pin, the end opposite the loop is spread apart with a screwdriver so that it can't work its way back through the hole during normal use of the linkage or threaded connection.

It is not necessary to spread and curl the ends of the pin in order to keep it in place. Simply spreading the pin a bit should do just fine to keep it from working it's way back out of the hole.

When holding a linkage in place, quite often a washer will be used in association with a pin. The pin keeps the washer in place, and the washer keeps the linkage rod or sleeve in place. Pins can be used with or without washers, depending on which approach will be more effective in distributing the loads and keeping the parts fastened together.

Done with Cotter Pins, back to Do It Yourself