AS9120B, ISO 9001:2015, AND FAA AC 0056B ACCREDITED

A Quick Guide to Cotter Pins

Cotter pins, cotter wedges, or split pins are small yet crucial locking components made up of thick wire with a semicircular cross-section inserted through a hole to join various parts of a machine. Examples of cotter pin use include securing a crank to its crankshaft or combining a piston rod to a crosshead. In a bicycle, a cotter pin locks the pedal crank to a bottom bracket axle to stop axial motion along the shaft when propelled into the assembly hole. For a steam engine, a cotter joint is tapered to resist thrust. The position of a component being held by a cotter pin is determined through the angle of the wedge. Hence, if the angle of the cotter pin is equal in both pedals on a bicycle, the pedal arms will be situated at a straight angle or 180 degrees from one another. While tapering into a hole, split pins usually get compressed, inducing friction and binding them tightly for security.

Cotter pins are easy-to-use fasteners utilized in many applications and require a drilled bolt, castle nut, and pliers for installation. Various cotter pins are available in multiple designs depending on the application. The most common type is the split cotter pin which is designed with a wire that creates a semicircle while bending over the flat portion of the pin to make the head like a small bulb. They are flexible pins available in different shapes and sizes depending on the bend of the wire. Moreover, cotter pins are designed to be one-time use fasteners that hold the clevis pin while inserted in a pre-drilled hole. Another type is the R-pin or spring cotter pin which is made from a metal wire with an R shape that usually fastens the shaft’s end, similar to how clevis pins are used to secure axles. An R-pin’s straight leg is inserted into a hole at the one end of the shaft, and the curved part remains outside as a hook attached to the shaft holds the pin in place. In addition, these are reusable pins and can be easily removed with one’s fingers.

A standard cotter is a type of pin with a large surface that provides a good grip when connecting to a machine. Curved or straight-shaped, standard cotter pins have two different ends where one end connects with the other pin and the second end connects with the component. Another type is a spring cotter pin which is designed in the shape of a spring that induces force to provide grip and deliver pressure on the component. The end part of the pin is developed in a T-shape that can be curved or straight depending on its application. Straight-designed pins are generally used for components with larger diameters as they need more surface area. Curved shape pins are used for smaller diameters as they can easily tighten on small surfaces with good curvature. One type is a barrel cotter pin with two ends, that of which includes one short and one long end designed in a cylindrical shape with rounded sides. Barrel cotter pins are used to fasten threaded joints, such as two hoses or pipes, together. Apart from these, there are three more categories of cotter keys available, including dripped cotter keys, straight cotter pins, and cotter pins with keys.

Dripped cotter pins have one flat-headed end with a hole while the other end is in a T-shape that can tightly fasten a dust cap to a mandrel around the shaft of the engine. Moreover, the straight cotter pin design has a cylindrical shape with straight ends with no round edges. These pins can mitigate frequent movement of components and prevent them from loosening. The last type is a cotter pin with T-shaped ends and an additional key which can be used to increase security.


Cotter pins are used to tighten threaded nuts and prevent them from loosening, ensuring the system's appropriate functionality. If you are searching for top-quality fasteners and cotter pins for your particular model of aircraft or other machines, we at Stacked Aviation can satisfy your requirements. Owned and operated by ASAP Semiconductor, Stacked Aviation is a prominent distributor of NSN, aerospace, and electronic parts for civil and military applications. With an inventory of over two billion new, used, and obsolete parts, we can fulfill your part requirements to support your operations while offering services with competitive pricing, lead times, and cost savings. If you are looking for specific parts for procurement, use our expert designed Instant RFQ service. A manager will call you back within 15 minutes after receiving your RFQ request. Contact us today; we are readily available to help you 24/7x365!


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