Width: Measure the diameter of the hole where the cotter pin needs to fit, and find a pin in the biggest possible size to fit in the corresponding material hole.

When choosing the best cotter pin for your application, consider: Pin lengths range from ¼ inch to 6 inches.

Our thickest pin measures 3/8 inches in width.

FMW Fasteners offers 18 cotter pin sizes to choose from, including small cotter pins that measure only 1/32 of an inch. If it's too narrow, the pin will wobble and compromise the assembly's stability. You want a pin that is long enough to reach all the way through the hole in the bolt with some left over for bending, but without so much extra length that it can't provide tension.Īdditionally, the pin needs to be the right diameter to fit into the bolt's hole and yield a lasting hold. When choosing the right size of the cotter pin, there are two dimensions to consider.

Fastening a nut on a motorcycle or vehicle wheel.

When the prongs of the pin are pulled well apart, they provide a stable hold and won't slip out.Ĭotter pins are ideal for use with bolts intended for machinery that moves or vibrates. Once the pin is all the way through the hole, you twist the ends of the pin outwards so that they pull away from each other. To attach a cotter pin to a compatible bolt, you simply slide it into the hole. Certain types of bolts are specifically designed for use with cotter pins and have pre-drilled holes for this purpose. The primary use for a cotter pin is to secure a bolt by slipping into a hole drilled in the bolt body. There are also different styles of cotter pins available, from extended prong pins to R-shaped pins. These U-shaped pieces of metal with a wide circular top can be made from stainless steel or zinc and come in a range of sizes. What Are Cotter Pins?Ĭotter pins, also known as split pins, are designed to hold bolts in place. When you need cotter pins that are going to work hard each day, just like you do, find the toughest cotter pins available when you choose FMW Fasteners as your supplier. A cotter pin is a two-pronged fastener made from metal that installs easily while providing structural support.įMW Fasteners offers both zinc-plated and stainless steel cotter pins. Save my name, email, and website in this browser for the next time I comment.Cotter pins, while simple in design, are infinitely useful when you need to keep pieces of machinery in place and secure over a period of time. This type of cotter has been largely replaced by splines and square shafts. This is used to draw the cotter into the hole and retain it in position. Cotters might have a threaded shaft protruding from the narrower end of the taper. Conventionally, it’s been used to attach cranks onto shafts (say, for example, on bicycles and steam engines). This brings us to the traditional cotter pin, which is a wedge that’s driven or drawn into a hole. Key rings are a common application for this type of fastener although they may also be used to retain pins and shafts. Essentially, it’s a wire loop that extends beyond 360 degrees allowing it to be threaded through a hole. Split ring: These components are also called a circle cotter or cotter ring. A finger can be inserted through the ring at the head to pull the pin out of the hole. The straight section may be pushed through a hole in a shaft, while the curved section clips around the outside of the shaft, retaining the pin in place. They’re sprung pins with a straight section that bends to form a ring at the head, with a curved section offset from the straight pin. R-clips or R-pins: These pins are sometimes referred to as hairpin cotters.

The bent end is formed into an enlarged end and the double end can be bent outwards to prevent the pin being removed. The pins are usually manufactured from a half-circular profile so that the two ends together form a circle, which fits into the hole. Split pins: Often called cotter pins, split pins are bent in half so that both ends may be inserted through the same hole. Here are a few of the different types of fasteners that are also considered cotter pins: However, the term “cotter pin” is also sometimes referred to as a split pin, an R-clip, or a circle cotter. The tapered nature of this pin means that it’s compressed as it is driven into the hole, causing friction, which prevents it from working loose. They’re either a wedge or tapered pin that’s driven into a hole. A selection of fasteners that are referred to as cotter pins (from left to right): Traditional tapered cotter as used on a steam engine, a cotter with a threaded section, as used on a bicycle crank, a split pin, an R-clip, and a split ring.Ĭotter pins are typically used to prevent axial movement along a shaft.