Cotter pin
Encyclopedia
A split pin, also known in U.S. usage as a cotter pin or cotter key, is a metal fastener
with two tines that are bent during installation, similar to a staple
or rivet
. Typically made of thick wire
with a half-circular cross section, split pins come in multiple sizes and types.
The British definition of "cotter pin" is equivalent to U.S. term "cotter
", which can be a cause for confusion when companies of both countries work together. There are signs that manufacturers and stockists are increasingly listing both names together to avoid confusion; this led to the term split cotter sometimes being used for a split pin.
A new split pin (see figure A) has its flat inner surfaces touching for most of its length so that it appears to be a split cylinder (figure D). Once inserted, the two ends of the pin are bent apart, locking it in place (figure B). When they are removed they are supposed to be discarded and replaced, because of fatigue
from bending.
Split pins are typically made of soft metal, making them easy to install and remove, but also making it inadvisable to use them to resist strong shear forces. Common materials include mild steel, brass
, bronze
, stainless steel
, and aluminium
.
Hammer lock split pins are properly installed by striking the head with a hammer to secure the pin. This forces the shorter tine forward, spreading the pin.
9 ^^
Split pins are frequently used to secure other fasteners, e.g. clevis pin
s, as well as being used in combination with hardboard
discs as a traditional joining technique for teddy bear
s.
Split pins may be used in some applications as low-tech shear pin
s. A common application of this is when used to secure a castellated nut
. One problem with this type of use is that the castles on the nut must line up with the hole in the mating part so that the split pin can be installed. When the nut is torqued properly, but the holes still do not line up, it is preferable to over-tighten the nut than under-tighten it.
Fastener
A fastener is a hardware device that mechanically joins or affixes two or more objects together.Fasteners can also be used to close a container such as a bag, a box, or an envelope; or they may involve keeping together the sides of an opening of flexible material, attaching a lid to a container,...
with two tines that are bent during installation, similar to a staple
Staple (fastener)
A staple is a type of two-pronged fastener, usually metal, used for joining or binding materials together. Large staples might be used with a hammer or staple gun for masonry, roofing, corrugated boxes and other heavy-duty uses...
or rivet
Rivet
A rivet is a permanent mechanical fastener. Before being installed a rivet consists of a smooth cylindrical shaft with a head on one end. The end opposite the head is called the buck-tail. On installation the rivet is placed in a punched or pre-drilled hole, and the tail is upset, or bucked A rivet...
. Typically made of thick wire
Wire
A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...
with a half-circular cross section, split pins come in multiple sizes and types.
The British definition of "cotter pin" is equivalent to U.S. term "cotter
Cotter
-People:*Cotter , an English, Irish and Americanized-German surname*Cotter , a medieval villein-Places:*Cotter, Arkansas, United States*Cotter, Iowa, United States*The Cotter River in the Australian Capital Territory-Other meanings:...
", which can be a cause for confusion when companies of both countries work together. There are signs that manufacturers and stockists are increasingly listing both names together to avoid confusion; this led to the term split cotter sometimes being used for a split pin.
Construction
Fatigue (material)
'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...
from bending.
Split pins are typically made of soft metal, making them easy to install and remove, but also making it inadvisable to use them to resist strong shear forces. Common materials include mild steel, brass
Brass
Brass is an alloy of copper and zinc; the proportions of zinc and copper can be varied to create a range of brasses with varying properties.In comparison, bronze is principally an alloy of copper and tin...
, bronze
Bronze
Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...
, stainless steel
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
, and aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
.
Types
As shown above, there are different types of ends available on split pins. The most common is the extended prong with a square cut, but extended prongs are available with all of the other types of ends. The extended prong type is popular because it makes it easier to separate the tines. To ease insertion into a hole the longer tine may be slightly curved to overlap the tip of the shorter tine or it is beveled. The length, L, of the split pin is defined as the distance from the end of the shortest tine to the point of the eyelet that contacts the hole.Hammer lock split pins are properly installed by striking the head with a hammer to secure the pin. This forces the shorter tine forward, spreading the pin.
- Standard
- Humped
- Clinch
Sizes
The diameter of split pins are standardized. American split pins start at in and end at in.| Nominal diameter [mm] | Hole size [mm] | For bolt size [mm] |
|---|---|---|
| 1.5 | 1.9 | 6 |
| 2 | 2.4 | 8 |
| 2.5 | 2.8 | 10 |
| 3 | 3.4 | 12, 14 |
| 4 | 4.5 | 20 |
| 5 | 5.6 | 24, 28 |
| 6 | 6.3 | 30, 36, 42 |
| 8 | 8.5 | 48 |
| Nominal diameter [in] | Hole size [in] | For bolt size [in] |
|---|---|---|
| 1, 1.125 | ||
| 1.25, 1.375 | ||
| 1.5 | ||
| 1.75 | ||
Applications
Clevis pin
A clevis fastener is a three piece fastener system consisting of a clevis, clevis pin, and tang. The clevis is a U-shaped piece that has holes at the end of the prongs to accept the clevis pin. The clevis pin is similar to a bolt, but is only partially threaded or unthreaded with a cross-hole for a...
s, as well as being used in combination with hardboard
Hardboard
Hardboard, also called high-density fiberboard , not to be confused with 'hardwood', is a type of fiberboard, which is an engineered wood product....
discs as a traditional joining technique for teddy bear
Teddy bear
The teddy bear is a stuffed toy bear. They are usually stuffed with soft, white cotton and have smooth and soft fur. It is an enduring form of a stuffed animal in many countries, often serving the purpose of entertaining children. In recent times, some teddy bears have become collector's items...
s.
Split pins may be used in some applications as low-tech shear pin
Shear pin
A shear pin is a safety device designed to shear in the case of a mechanical overload, preventing other, more-expensive parts from being damaged...
s. A common application of this is when used to secure a castellated nut
Castellated nut
A castellated nut, also called a castle nut or slotted nut, is a nut with slots cut into one end. The name comes from the nut’s resemblance to the crenellated parapet of a medieval castle....
. One problem with this type of use is that the castles on the nut must line up with the hole in the mating part so that the split pin can be installed. When the nut is torqued properly, but the holes still do not line up, it is preferable to over-tighten the nut than under-tighten it.