Understanding Knuckle Joint

The knuckle joint connects two rods whose axes either coincide or intersect and are in the same plane. They’re commonly found in tractor-trailers, roof truss tie rods, suspension bridge link joints, and steering systems, where they’re found between the steering rod and pinion. In this article, you’ll learn the definition, applications, diagram, design, construction, components, types, working, advantages, and disadvantages of knuckle joints.

Knuckle Joint


What is a Knuckle Joint?

When a tiny amount of flexibility or angular moment is required, a knuckle joint is a mechanical junction used to connect two rods that are under a tensile load. Axial or linear lines of load action are always present. It is used to connect two rods that are under the action of tensile loads. However, if the joint is guided, the rods may support a compressive load. For modifications or repairs, a knuckle joint can be easily separated. It can be found in a cycle chain link, a tie rod joint for a roof truss, a valve rod joint with the eccentric rod, a pump rod joint, a tension link in a bridge structure, and a variety of lever and rod connections.

Applications of Knuckle Joint

Knuckle joint is commonly used in the automotive industries to make the following joints:

  • The link in the cycle chain
  • Roof truss tie rod joints
  • Tension link in bridge structure
  • Various types of lever and rod connections.
  • In multi-axle vehicles, the link rod of the leaf springs is connected
  • Connections between the leaf spring and the chassis
  • Piston, piston pin, connecting rod

Diagram of a Knuckle Joint:


Components of a knuckle joint

The major part of a knuckle joint is the eye, fork, & pin. Other components include;

  • Two rods – The knuckle joint is normally connected by two rods. One rod has an eye on one end, while the other has two fork-like ends.
  • Double-eye End or Fork EndThe double-eye end is usually made up of two ends and has a fork-like shape. Because one end is used to insert the knuckle pin and the other is used to insert the taper pin into the collar, the joint does not open.
  • Single-eye EndThe single-eye end of the two holes is inserted between the double-eye end of the two holes, bringing all three holes together (2 holes from the double-eye end and 1 hole from the single-eye end).
  • Knuckle Pin – The knuckle pin is inserted into these holes and tightly connects them together. The taper pin is usually inserted through a tiny hole at the end of the knuckle pin.
  • Collar – It has a collar with two holes for the taper pin to pass through. The collar is positioned at the end of the knuckle pin so that the hole at the knuckle joint meets the hole in the collar.
  • Taper Pin – To attach the collar and knuckle pins and prevent them from slipping, a taper is placed through the hole of the collar.
  • Knuckle-Joints-Components

Construction and Material

One end of one of the rods is shaped into an eye in the knuckle joint (two views shown in Fig.) and the other end of the rod is created into a fork with an eye in each of the fork legs.
The knuckle pin is attached with a collar and taper pin or a spilled pin and runs through both the eye and fork holes. A small stop, pin, peg, or snug can be used to keep the knuckle pin from turning in the fork.

On one of the rods, the eye is formed, and on the other, the fork is formed. The eye is inserted into the fork, and the pin is threaded through the fork and eye. A split pin is used to keep this pin in its place. The rods’ ends are octagonal for a short distance for improved grip and square for a short distance before being forged into the eye and fork shapes.

Aluminum, stainless steel, structural steel, magnesium, and cast iron are common materials used in knuckle joints. Aluminum knuckle joints have been shown to offer the maximum safety factor of roughly 50 kN under loading situations.

Some businesses utilize a combination of cast iron and stainless steel for their joints. Material costs and weight have decreased as technology has advanced in recent decades, resulting in fewer accidents and better safety. It was recently discovered that using composite material instead of cast iron has a number of benefits, including easy-to-make knuckle joints, optimum safety, and environmental friendliness. The knuckle joint can be simply cast, manufactured, and forged.

Watch the video below to learn more about the working of a knuckle joint:

Advantages and Disadvantages of a Knuckle Joint


Below are the benefits of a knuckle joint in its various applications.

  • Knuckle joints can bear significant tensile strains. Even with variable material thickness and tensile strength, it may provide excellent repetitive accuracy.
  • They have a high degree of mechanical stiffness.
  • They have a straightforward design and are simple to set up.
  • The knuckle joint is simple to put together and take apart.
  • The knuckle joint’s construction is simple to build.
  • This joint has fewer pieces, which makes it less expensive and more reliable.
  • This provides for angular momentum between rods and is mostly used to extend the tool’s life.


Despite the good advantages of knuckle joints, some limitations still occur, below are the disadvantages of a knuckle joint.

  • The ability of knuckle joints to endure large compressive loads is limited.
  • It provides angular momentum in one plane only. One of their flaws is this.
  • You may have tested their flexibility using a universal joint, but the knuckle joint lacks such flexibility.

Related Article:


When a little degree of flexion or angular movement is required, a knuckle joint is used to connect two rods under tensile loads. That is all for this article, where the definition, applications, diagram, design, construction, components, types, working, advantages, and disadvantages of knuckle joints are discussed. I hope you get a lot from the reading, if so, kindly share with other students. Thanks for reading, see you around!

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