What Are Rod Ends and How Are They Used?

What Are Rod Ends and How Are They Used?

by Kevin Sweeney
04 August, 2023
11 min read

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 is 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.

Self lubricating, Standard Series  Rod End, Female

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.

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.

Pacific International Bearing Inc offers the industry’s widest selection of rod end types and sizes.

The product range includes:

  • Rod ends with brass race inserts in standard, precision and high capacity designs;
  • High strength two piece designs;
  • Self-lubricating rod ends with engineered thermoplastic races or high performance Teflon® liners, military standard rod ends for the ultimate in rod end performance. 

The spherical  ball bearing rod ends have extremely low friction and misalignment capability, and elastomeric bearing rod ends  reduce vibration and noise. 

The ability of rod ends to articulate and accommodate angular misalignment is a key feature, allowing them to compensate for installation errors, structural deflections, and dynamic movements. The angle of misalignment can vary depending upon the size and can in some cases be ordered and manufactured to the customer specifications. 

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 fracture tough head, ductile shank, and a carburized raceway. These steps are done so as 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 that 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 the selection of rod ends. 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.

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.

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Written by

Kevin Sweeney

Founder and CEO at Pacific International Bearing Sales Inc (PIB)
Education: BS Business and Economics California State University Hayward Ca
CBS (Certified Bearing Specialist)

My role with Pacific International Bearings (PIB) is currently CEO. Since 1976, I have been deeply involved in the bearing industry, working in manufacturing sales at NTN Bearing and subsequently in Bearing Distribution. Before establishing PIB in 1990, I gathered valuable experience in bearing manufacturing and distribution. The last 45 + years in the bearing industry have been both rewarding and challenging, assisting customers across a large number of diverse bearing applications.
Outside of the bearing industry, my interests are family, woodworking, motorcycling, cars, gardening, and golf.
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