A cotter pin is a cheap and simple fastener made of soft metal used to lock low-torque parts in place. It comes in different sizes and designs, and once in place, the legs are bent back to prevent it from coming loose. It is commonly used in automobile hubs and can only be used once.
A cotter pin is a simple fastener usually made of soft, malleable metal used to lock low-torque parts in place. The cotter pin typically consists of a flat, round, or semi-circular pin bent in half with a pronounced ring at the closed end. After a part has been seated, the pin is passed through a hole in the shaft and one or both of its “legs” are bent back to prevent it from coming loose while the ring on the closed end prevents it from falling through. the hole. If the part needs to be removed, the bent legs of the pin are simply straightened and the cotter pin removed.
Cotter pins are among the cheapest and most widely used fasteners for low-speed, low-stress parts. They can be found in a myriad of applications ranging from brake disc locks on heavy vehicles to paper puppets and plush joints. Also known as cotter pins, these fasteners come in a range of sizes and designs, including straight pins, spring pins, and hammer lock pins. Different cross section profiles such as round, flat or half round are also available. The cotter pin is also available with different end profiles including chamfered ends, angled ends and extended point pins, all suited to specific uses.
Part of the beauty of using cotter pins as fasteners is their sheer simplicity. Once the part to be locked is in place, the pin is pushed through an adjacent locking hole until the end ring or eyelet locks it further. One or both legs are then bent back to prevent the pin from coming loose, thus effectively preventing the part from slipping out of its seat or coming off the shaft. There are some cotter pin designs, such as the spring pin, that are a little more sophisticated. These pivots feature a spring steel frame and a “belly” profile in one of the legs that locks around the outer surface of the round shafts.
One of the well known uses of the cotter pin is the locking mechanism of the lug nuts commonly used on automobile hubs. These lightweight nuts lock the hubs in place and exert adequate torque on the wheel bearings. They feature a series of raised tabs along the upper edges resembling castle battlements. The stub axle has a hole through it, and once the nut is tightened to the correct torque, the cotter pin is inserted through the hole between the tabs on the nut. The ends are then bent back to lock the pin and prevent the castle nut from coming loose.
The materials used in manufacturing cotter pins tend to be soft, malleable metals such as aluminum, bronze, brass, and mild steel. This allows the legs to fold easily when locking the pin in place. Unfortunately it also means that the legs will only survive being bent once or twice before snapping. For this reason the pins must be used only once and then discarded; this is quite acceptable when you consider the low cost of these versatile little fasteners.
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