What Are Rod Ends and How Are They Used?

The words Heim Joints are synonymous with Rod Ends since Lewis Heim invented them and founded the Heim Bearing Company, currently a subsidiary of RBC Bearing Company. Rod Ends are spherical plain bearings mounted in a housing with a connected rod. Rod ends are commonly used in linkages and are very easy to mount and install. They are commonly used in agriculture, lawn and garden, ground power, material handling, fluid power, and in automotive racing and standard vehicles. 

RBC Heim bearings is the leader and offers the largest selection of rod end types. The vast product range for RBC Heim includes Rod Ends having brass inserts in standard and higher capacity and precision designs. Heim bearings are the leader in offering the two piece, self-lubricating with Teflon® liners. RBC Heim rod ends offer low friction and misalignment features along with a variety of coatings and material types available. Rod ends can be ordered with lubrication fittings, left or right hand threads, and keyways.

Pacific International Bearing offers RBC Heim Rod ends in both metric and inch series that can be purchased on our online store.

Overview of Rod Ends

Rod ends are sometimes referred to as spherical plain bearings. The images below are spherical plain bearings differing from Rod Ends as they have no connecting rod to the outer housing shell.

Rod End bearings provide articulation and rotational movement in mechanical systems and are ideal in robotic and automotive linkage applications. Rod Ends are constructed with a housing or body, a ball, and a race. The spherical ball can be steel on steel or is often manufactured with a liner as in the third image above.

As I mentioned, the first integral rod end was invented by Lewis Heim and so spherical Rod end bearings due to Heim became the industry standard for spherical bearings. The Heim Joint as it was called became so pervasive in the market that it became that spherical bearings were known as Heim Joint bearings.

Buy Spherical plain bearings from PIB.

What are the Components of Rod Ends?

Rod ends are designed to facilitate both rotational motion and angular misalignment, making them essential in applications like automotive suspensions and industrial machinery. To fully understand how rod ends function and why they are so effective, it’s important to explore their key components and how each part contributes to the overall performance.

Ball

The ball is the central component of a rod end. This spherical element allows the joint to rotate and pivot, enabling the necessary angular and rotational movements.

• Typically manufactured from high-grade steel or stainless steel, chosen for their strength and resistance to corrosion. Chrome plating or other surface treatments are often applied to reduce friction and enhance durability.
• The ball is ground to precise tolerances, generally within ±0.01 mm, ensuring smooth operation. Common ball diameters range from 5 mm to 25 mm, depending on the application.

Inner ring

The inner ring, or inner race, surrounds the ball and provides a smooth surface for its movement.

• Usually made from case-hardened steel, which offers a good balance of toughness and wear resistance. Some variants may use specialty alloys or ceramic materials for enhanced performance.
• The inner ring’s bore and outside diameters are precision-machined to match the ball’s size, typically ranging from 4 mm to 20 mm. Surface roughness is controlled, often with a roughness average (Ra) of 0.4 µm or better.

Outer ring (housing)

The outer ring, also known as the housing, encloses the ball and inner ring, providing the structural integrity needed for the rod end to perform under load.

• Commonly constructed from forged steel or stainless steel, with zinc plating or other corrosion-resistant coatings. Aluminum alloys are sometimes used for lightweight applications.
• The housing is threaded for easy mounting, with metric thread sizes typically ranging from M6 to M30. The housing may also include lubrication grooves or holes to facilitate maintenance.

Race

The race is the hardened surface within the outer ring that directly contacts the ball, allowing the rod end to handle both rotational and angular movements effectively.

• Made from hardened steel, often treated to enhance wear resistance.
• Precision-ground to fit tightly with the ball, ensuring minimal play and high load-carrying capacity. The hardness is usually specified between 58 to 62 HRC on the Rockwell scale.

Stud (Optional)

In some rod end designs, a stud is integrated into the outer ring, extending the mounting options.

• Typically constructed from high-strength steel, with surface treatments such as zinc or phosphate coatings for additional corrosion resistance.
• Studs are available in various lengths and thread sizes, conforming to ISO metric or UNC/UNF thread standards. These studs can support significant loads, depending on the material and design.

Rod ends are easy to mount and can be adjusted during installation easily. Rod Ends are of a compact design incorporating the misalignment features of spherical bearings.

Fit Classification (`1,2 or3)  No-Load Breakaway Torque (in-lb) Explanation

• (1) 6.0 – 24.0 Extremely tight. Users may need the assistance of mechanical advantage/leverage, such as a steel bar through the bore, to move the ball.
• (2) 2.0 – 6.0 Moderately tight. Users should be able to move the ball by hand, but noticeable resistance will be felt.
• (3) 0.0 – 1.0 No clearance present in the bearing. However, the ball will move freely with light to moderate finger pressure, with very light resistance felt.

PTFE lined bearings are self-lubricating and maintenance free.

Number (2) is the Industry standard fit but check with PIB  as each Manufacturer may use a slightly different breakaway torque value. 

Contact Pacific International Bearing to obtain the correct clearance fit when ordering.

What are the Various Types of Rod Ends?

Pacific International Bearing Inc offers one of the industry’s most comprehensive selections of rod end types and sizes. Their extensive product range includes:

• Rod ends with brass race inserts are available in standard, precision, and high-capacity designs. Brass inserts provide excellent wear resistance and are ideal for applications requiring low friction and good load distribution.
• High-strength two-piece designs are built for heavy-duty applications, featuring separate body and ball components that allow for higher load capacities and increased durability.
• Self-lubricating rod ends are equipped with engineered thermoplastic races or high-performance Teflon® liners, these rod ends reduce the need for maintenance by providing consistent lubrication, which enhances their lifespan and performance under repetitive motion.
• Military standard rod ends designed for the ultimate performance in extreme conditions, these rod ends comply with military specifications, offering enhanced strength, corrosion resistance, and precision suitable for aerospace and defense applications.
• Spherical ball bearing rod ends known for their extremely low friction and high misalignment capability, these rod ends are perfect for applications where smooth, consistent rotation and flexibility are required.
• Elastomeric bearing rod ends incorporate elastomeric materials that effectively reduce vibration and noise, making them ideal for dynamic applications where shock absorption is critical.

Rod ends are designed to articulate and accommodate angular misalignment, a key feature that allows them to compensate for installation errors, structural deflections, and dynamic movements. The misalignment angle can vary depending on the rod end size, with typical ranges from 5° to 20°, and can be custom-manufactured to meet specific customer requirements. This adaptability makes rod ends highly versatile, ensuring optimal performance even in challenging mechanical environments.

Additionally, rod ends can be customized with various coatings, such as zinc plating or phosphate coatings, to enhance corrosion resistance and longevity. Some models also offer specialized sealing options to prevent contamination and extend service life in harsh environments.

Benefits of Rod Ends

Rod ends offer several distinct advantages that make them highly effective in mechanical and industrial applications:

1. Compensation for misalignment

Rod ends are uniquely designed to handle angular misalignments in mechanical linkages. This capability allows them to absorb installation errors, structural deflections, and dynamic movements, ensuring smooth operation even when components are not perfectly aligned. This flexibility reduces the risk of premature wear and damage to connected parts.

2. High strength and load capacity

With robust materials like high-grade steel and precision-engineered components, rod ends can support significant loads and stresses. Their design ensures reliable performance in high-load scenarios, such as in heavy machinery or automotive suspensions, where durability and strength are crucial.

3. Self-lubricating for reduced maintenance

Many rod ends incorporate self-lubricating features, such as Teflon® liners or thermoplastic races, which reduce the need for regular lubrication. This self-lubrication minimizes friction, lowers wear rates, and extends the component’s life, making rod ends particularly advantageous in applications with limited maintenance access.

4. Noise and vibration dampening

Some rod ends include elastomeric bearings or specialized liners that absorb vibrations and reduce noise. This is especially beneficial in dynamic systems like engines or moving machinery, where minimizing vibrations enhances performance, reduces noise pollution, and prevents damage from repetitive stresses.

Due to the unique construction and functionality of rod ends, engineers can make informed decisions during selection resulting in optimal results.

Functionality and Working Principles

The ball, housed within the race, provides a low-friction contact surface, enabling rotational movement with minimal resistance. The working angle, represented by the maximum angular range, determines the extent to which the rod end can accommodate misalignment and dynamic movements.

This angle can be calculated using the formula:

• θ = tan^(-1)(d / D),
• where θ is the working angle,
• d is the diameter of the ball,
• D is the diameter of the race.

The functionality of rod ends is influenced by proper lubrication or the use of liners. Factors such as viscosity, additives, and temperature stability must be considered when selecting the appropriate lubricant. Furthermore, advancements in lubrication techniques, such as self-lubricating rod ends, have emerged, eliminating the need for frequent maintenance and lubricant replenishment.

The versatility of rod ends is demonstrated by the wide range of applications across various industries. In automotive systems, rod ends are employed in steering linkages, suspension components, and throttle systems, where precise articulation and load transmission are critical. 

In aerospace applications RBC rod ends are utilized in control surfaces, landing gear assemblies, and actuation systems, requiring robust and reliable components that can withstand extreme operating conditions and stringent performance requirements. Additionally, industrial machinery, marine equipment, agricultural machinery, and construction equipment all benefit from rod ends in various applications where durability, load capacity, and flexibility are essential. 

Pacific International Bearing stocks and distributes RBC Rod End Bearings meeting Mil Spec Standards. RBC manufactures a line of Mil Spec specialty and custom ball bearing rod end anti-friction bearings. RBC’s double-row, self-aligning bearings accommodate various application’s low torque, high load, and misalignment needs. RBC Mil Spec Rod Ends conform to SAE-AS6039, formerly MIL-B-6039.

RBC’s double-row self-aligning rod ends have inner rings and balls made from thru-hardened 52100 or 440C stainless to accommodate corrosion resistance needs.  These bearings are lubricated 80 to 100% fill in compliance with MIL-PRF-81322, MIL-PRF-23827, and Boeing’s BMS3-33 specifications. RBC  Ball bearing rod ends are manufactured with PTFE seals bonded to corrosion resistant caps.

RBC’s rod end body is heat treated to provide a combination of a fractured tough head, ductile shank, and a carburized raceway. These steps are done to provide for a higher load-carrying capacity than lower cost less manufactured products in the marketplace. RBC manufactures so that the external surfaces are plated with cadmium to provide corrosion protection and thread lubricity.  The rod end body can be supplied to AISI8620 or RBC’s proprietary AeroCres® corrosion resistant material. Buy RBC from Pacific International Bearing Sales Inc.

Understanding the functionality and working principles of rod ends is important for engineers and professionals involved in the design and maintenance of mechanical systems. By considering factors such as the ball-and-socket joint design, lubrication techniques, liner options, load capacity, and industry-specific requirements, engineers can select and integrate rod ends effectively, ensuring optimal performance, longevity, and safety in diverse applications.

Considerations for Rod End

Selecting the appropriate rod end for a specific application requires careful consideration of several factors to ensure optimal performance, reliability, and safety:

• Load Capacity

Determining the maximum load a rod end can withstand without compromising performance is crucial. The load capacity depends on factors such as the ball size, material properties, and the design of the race and housing. Engineers can utilize formulas, such as the dynamic load rating (C) and the static load rating (Co), to assess the load-carrying capability of rod ends.

• Misalignment Capability

Rod ends are designed to accommodate angular misalignment, allowing for flexibility in mechanical linkages. The maximum angular misalignment a rod end can handle is determined by its design and specifications. Engineers should consider the specific misalignment requirements of the application to ensure proper functionality and longevity.

• Temperature Range

The operating temperature range plays a critical role in rod end selection. Extreme temperatures can affect the performance and lifespan of the components. Engineers should consider the coefficient of thermal expansion, the maximum and minimum operating temperatures, and the potential for thermal variations in the application environment.

• Environmental Conditions

Environmental factors such as moisture, chemicals, dust, and vibrations can impact the performance and durability of rod ends. Engineers should assess the application environment and select rod ends with appropriate corrosion resistance, sealing mechanisms, and protective coatings to ensure long-term reliability.

• Maintenance Requirements

Proper maintenance is essential for the optimal performance and longevity of rod ends. Engineers should consider factors such as lubrication intervals, inspection schedules, and accessibility for maintenance tasks. Regular inspections can help identify signs of wear, lubrication deficiencies, or other issues that may affect the performance of the rod ends.

Contrarily Rod Ends with self-lubricating teflon or other materials considerably reduces lubrication issues and maintenance concerns.

FAQ’s

Q: How are rod ends measured?
A: Rod ends are measured by their thread size, bore diameter, and overall length. Thread size (e.g., M6) determines attachment, bore diameter matches the connecting pin or shaft, and overall length includes the threaded shank and body, ensuring proper fit and function.

Q: What are the main parts of a rod?

A: Rod ends consist of a ball for pivoting, an inner ring for smooth movement, and an outer ring (housing) for support and mounting. The race inside the housing contacts the ball directly, facilitating movement. Some designs include an optional stud for additional mounting.

Q: How long do tie rods last?

A: Tie rods, including those with rod ends, typically last 50,000 to 100,000 miles, but lifespan varies with driving conditions and maintenance. Regular inspections and lubrication help extend their life; signs of wear should prompt replacement for safety.

Final thoughts

The versatility of rod ends makes them useful in many applications such as automotive, industrial, aerospace, marine, agricultural, and construction equipment. Applications include steering linkages, suspension systems, robotics, manufacturing equipment, control surfaces, rudder systems, and hydraulic cylinders. 

Ongoing Rod End bearing research and material advancements hold promising prospects for future improvements. Most  Rod End Bearing manufacturers conduct ongoing research focusing on improving materials, lubricity, and design, aiming to enhance performance, durability, and sustainability.

Still have a question or need to discuss something? Contact us to get help.