Joints & Linkage Components

What are joints and linkage components?

Joints and linkage components are the connecting parts used to link rods, levers, cylinders, and moving mechanisms together, allowing motion and force to be passed from one part of a machine to another. They are found wherever something needs to be pushed, pulled, tilted, or turned through a linkage, such as control rods, throttle and gear linkages, gas springs, actuators, steering mechanisms, and adjustable machine parts.

Different joints allow different types of movement. A clevis creates a hinged joint that pivots in one plane, a ball joint allows movement in several directions, and a universal joint transmits rotation through an angle. Together, these components make it possible to build linkages that move smoothly, accurately, and reliably, even when parts are not perfectly aligned.

Common joints and linkage components include:

• Clevises (fork heads) - U-shaped fittings with a pin that create a hinged joint on the end of a threaded rod
• Clevis pins - pins that pass through the clevis and the connected part, often secured with a spring clip or split pin
• Ball studs - threaded studs with a ball on one end, forming the ball half of a ball joint
• Ball sockets - fittings that clip over a ball stud, creating a ball and socket joint that can move in several directions
• Angle joints - ball joints with the ball and socket set at an angle, ideal for linkages that move through an arc
• Rod ends - spherical bearings in a threaded housing, allowing angular movement under higher loads
• Universal joints - joints that transmit rotation between two shafts set at an angle

Key features:

• Connects moving parts - links rods, levers, cylinders, and mechanisms together
• Allows controlled movement - hinged, swivelling, or angled movement depending on the joint
• Compensates for misalignment - ball joints and rod ends tolerate angular movement
• Adjustable length - threaded ends allow linkages to be lengthened or shortened for precise set-up
• Right- and left-hand threads - used together to adjust linkage length by turning the rod
• Easy to fit and remove - clips, pins, and threaded connections make assembly and maintenance quick
• Standardised sizes - many components follow DIN standards, so parts are interchangeable
• Range of materials - zinc plated steel, stainless steel, and plastic options

In simple terms, joints and linkage components are the connectors that let rods and levers move, pivot, and swivel together smoothly.

Why are joints and linkage components essential?

Joints and linkage components are essential because almost every mechanism with levers, rods, or actuators relies on them to transfer movement. If a joint is worn, loose, or the wrong type, the linkage can develop play, bind, wear quickly, or fail completely, leading to poor control, inaccurate movement, and breakdowns. Choosing the right joint for the movement and load keeps mechanisms working smoothly and precisely.

Their main benefits are:

• Smooth movement - allows parts to pivot, swivel, and tilt freely without binding
• Accurate control - well-fitting joints reduce play, giving precise and responsive linkages
• Misalignment compensation - ball joints and rod ends accommodate angles and small alignment errors
• Adjustability - threaded connections allow linkage length and position to be fine-tuned
• Reduced wear - the correct joint spreads loads and reduces wear on rods, levers, and pivots
• Quick maintenance - clip and pin connections allow linkages to be disconnected and reconnected easily
• Versatility - a wide range of joint types suits almost any linkage design
• Cost-effective - standard components are economical and easy to replace

Joints and linkage components are used across a wide range of industries and applications, including:

• Agricultural machinery - control linkages, hitches, levers, and implement adjustments
• Industrial machinery - control rods, levers, guards, and adjustment mechanisms
• Pneumatic and hydraulic cylinders - connecting cylinder rods to the parts they move
• Gas springs and dampers - mounting gas struts on lids, hatches, and machine guards
• Automotive and transport - throttle, gear, and choke linkages, and adjustable mechanisms
• Packaging and food machinery - linkages, actuators, and adjustable guides
• Automation and robotics - actuators, grippers, and moving mechanisms
• Marine - steering, throttle, and control linkages
• Model engineering and hobby projects - small linkages and control mechanisms

The main types of joints and linkage components

Joints and linkage components are usually grouped by the type of movement they allow.

Clevises and pins:

• Clevises - also called fork heads, these U-shaped fittings screw onto a threaded rod and connect to a lever or bracket with a pin, creating a joint that pivots in one direction. Many follow the DIN 71752 standard
• Clevises with spring clip pins - supplied with a self-retaining pin that clips into place without tools, allowing quick connection and removal
• Quick-release clevises - designed for fast disconnection without removing the pin completely
• Clevis pins - plain pins with a head and a hole for a split pin, or grooved pins for retaining clips
• Safety clips and split pins - secure clevis pins so they cannot work loose

Ball joints:

• Ball studs - threaded studs with a ball on one end. They screw into a lever, bracket, or rod, providing the ball for a ball and socket joint. Common ball sizes include 8, 10, 13, 16, and 19 mm, each paired with a matching thread size
• Ball sockets - fit over the ball stud and are held on with a spring clip, allowing movement in several directions. Many follow the DIN 71805 standard
• Angle joints - combine a ball stud and ball socket set at an angle, ideal for linkages that move in an arc, such as throttle and control linkages. Many follow the DIN 71802 standard
• Safety clips - secure ball sockets onto ball studs to prevent accidental separation

Rod ends:

• Rod ends - spherical plain bearings in a threaded eye-shaped housing, used where higher loads and larger angular movements are needed, such as on cylinder rods and heavy-duty linkages
• Male and female thread rod ends - fit either onto or into a threaded rod

Universal joints:

• Single universal joints - transmit rotation between two shafts at an angle
• Double universal joints - allow larger angles and smoother rotation between shafts
• Plain bearing and needle bearing universal joints - plain bearing types suit slower or occasional use, while needle bearing types suit higher speeds and continuous operation

By thread direction:

• Right-hand thread - the standard thread direction, tightened clockwise
• Left-hand thread - tightened anticlockwise. Using a left-hand joint on one end of a rod and a right-hand joint on the other allows the linkage length to be adjusted simply by turning the rod

By material:

• Zinc plated steel - strong and economical, with good corrosion protection for general use
• Stainless steel - corrosion resistant, ideal for food, marine, and outdoor environments
• Plastic - lightweight, corrosion resistant, and quiet, suitable for light loads

How to choose the right joints and linkage components?

Choosing the right joints and linkage components means matching them to the movement, load, and size of the linkage. Work through these points in order:

• Type of movement - choose a clevis for hinged movement in one plane, a ball joint or angle joint for movement in several directions, a rod end for higher loads and larger angles, or a universal joint for rotating shafts at an angle
• Thread size - match the thread of the joint to the rod, lever, or cylinder, such as M5, M6, M8, or M10
• Thread direction - choose right-hand or left-hand threads, and use a combination of both where the linkage needs length adjustment
• Male or female thread - check whether the joint needs to screw onto a rod or receive a threaded stud
• Ball size - for ball joints, make sure the ball stud and ball socket sizes match
• Pin size and fork width - for clevises, check the pin diameter, fork width, and fork length suit the connected lever or bracket
• Load - choose stronger components, such as rod ends or larger clevises, for heavy or shock loads
• Angle of movement - check the joint allows enough angular movement without binding
• Retention - choose spring clip pins, safety clips, or split pins to stop joints coming apart
• Material - choose zinc plated steel for general use, stainless steel for corrosive or hygienic environments, or plastic for light, quiet linkages
• Standards - choose components made to recognised DIN standards for reliable interchangeability
• Quality and brand - choose components from reputable suppliers for accurate threads, smooth movement, and long service life

FAQ - All you need to know about joints and linkage components

What is a clevis used for?

A clevis is a U-shaped fitting that screws onto a threaded rod and connects to a lever, bracket, or cylinder with a pin. It creates a hinged joint that pivots in one direction.

What do the numbers on a clevis mean?

Clevis references usually describe the size of the pin and thread and the length of the fork. For example, a G6 × 12 clevis is sized for a 6 mm pin and thread, with a 12 mm fork length. Always check the full dimensions before ordering.

What is the difference between a ball joint and a clevis?

A clevis allows movement in one direction, like a hinge. A ball joint allows movement in several directions, making it ideal for linkages that move at changing angles.

What is a ball stud?

A ball stud is a threaded stud with a ball on one end. It screws into a lever or bracket and fits into a ball socket to create a ball and socket joint.

How do I choose the right ball stud and socket?

Match the ball diameter of the stud to the socket, and choose the thread size that suits your lever, rod, or bracket. For example, a 16 mm ball stud may have an M10 thread.

What is an angle joint?

An angle joint is a ball and socket joint where the socket sits at an angle to the threaded shank. It is ideal for linkages that move through an arc, such as throttle and control linkages.

What is the difference between a ball joint and a rod end?

A ball joint is a compact joint for lighter loads and linkages. A rod end contains a spherical plain bearing and is designed for higher loads and larger angular movement.

Why use left-hand threads?

Fitting a left-hand thread joint on one end of a rod and a right-hand thread joint on the other lets you adjust the length of the linkage by simply turning the rod, without disconnecting either end.

How do I stop a ball socket coming off a ball stud?

Use the spring clip supplied with the ball socket, or fit a safety clip. These hold the socket onto the ball while still allowing movement.

Do joints and linkage components need lubrication?

Many joints benefit from occasional lubrication to keep them moving smoothly and to reduce wear. Some plastic and maintenance-free joints do not need lubrication, so check the manufacturer’s guidance.

How do I know when a joint needs replacing?

Signs include play or looseness, rattling, stiff or rough movement, worn or oval pin holes, damaged threads, and corrosion. Worn joints should be replaced to keep the linkage accurate and safe.