- By Profab /
- August 1, 2025
Rod ends, also known as Heim joints or spherical rod ends, are typically made up of three main elements: an outer spherical shell, a ball, and a rod. Rod ends are generally categorized by design, lubrication type, thread type, and divided by material.
Table of Contents
By Lubrication Type
Rod ends are primarily classified according to their design, in particular their lubrication method and structural characteristics.
Self-Lubricating Rod End Bearings
These rod ends feature a specialized internal lining that provides continuous lubrication throughout their service life and are most commonly made from high-performance polytetrafluoroethylene (PTFE) or engineered thermoplastics.
- Material: The housing is usually made of carbon steel, alloy steel or stainless steel. The sliding layer can be PTFE composite material or PTFE film.
- Load capacity: Capable of accommodating radial loads in both tension and compression. Particularly suitable for slow motion applications involving small to medium swing angles and unilateral loads.
- Temperature range: PTFE-lined rod ends typically perform best in a temperature range of -65°F to 325°F (-54°C to 163°C). Other self-lubricating types can operate in temperatures from -50°C to +200°C, but it is worth noting that their load-carrying capacity is reduced above 120°C.
- Advantage: Lower maintenance requirements and operating costs; longer service life and higher performance. Effective vibration and noise reduction
- Application: These rod ends are widely used in systems with frequent motion or vibration, such as aerospace and military applications.
Greaseable Rod End Bearings (With Grease Nipple)
These rod ends are designed with integrated grease nipples to allow for regular relubrication. Their bronze raceways are usually divided into two sections to facilitate the inclusion of oil grooves, ensuring efficient grease distribution.
- Material: The housing is typically carbon steel, silver-zinc plated for corrosion resistance. They typically feature bronze raceways and 52100 bearing steel balls. For larger sizes, the housing may be made of forged QT (quenched and tempered) steel, providing enhanced strength.
- Load capacity: These rod ends are specifically designed to handle heavy radial loads and can effectively manage combined loads, provided that the axial load component does not exceed 20% of the corresponding radial load.
- Temperature range: Rod ends with integral spherical plain bearings are rated for temperatures between -30°C and +60°C. However, higher temperatures result in a reduction in their load capacity.
- Advantage: Rugged and durable, they are suitable for heavy-duty applications, especially those exposed to high levels of dust, water, or other contaminants. Regular lubrication helps remove these abrasive particles and prolongs component life.
- Application: Commonly used in agricultural machinery, gardening equipment, pneumatic and hydraulic systems, fitness equipment, and various types of lifting equipment.
Metal-To-Metal Rod Ends
This is the simplest form of rod end bearing design. In this configuration, the spherical inner ring slides directly on the metal surface of the inner ring, with no internal lubrication or lining.
- Material: The housing is typically made of carbon steel, often silver or yellow zinc plated to provide basic corrosion resistance. The ball can be carbon steel or 52100 bearing steel.
- Load capacity: Known for their inherent high strength, these rod ends are a rugged choice for demanding static load applications.
- Temperature range: They are particularly effective in high-temperature environments. The steel-on-steel sliding contact surface can operate over a wide temperature range of -50°C to +200°C. Special versions can handle temperatures up to 300°C upon request. Please note that above 120°C, the load-bearing capacity may be reduced.
- Advantage: Especially suitable for applications requiring high strength and operating in high temperature environments where traditional lubricants may degrade or fail.
- Application: Best suited for fixed-position components, applications in high-temperature environments, and where component strength is an absolute priority.
According To Structural Design
Two-Piece Rod End Bearings
These rod ends feature a separate outer shell and a spherical inner ring.
- Features: They are known for allowing significant articulation and being able to achieve high load ratings. This design can be used to accommodate greater angular motion, which is critical for certain dynamic applications. Some can even provide up to 64 degrees.
- Material: The housing is typically made of carbon steel (often silver-zinc plated) or alloy/chrome-molybdenum steel (heat-treated and zinc-plated). The spherical inner ring is typically 52100 bearing steel, and the raceways are often PTFE-lined. Stainless steel options (e.g., 304, 440C chrome-plated) are also available for enhanced corrosion resistance.
- Load capacity: They are designed for heavy-duty applications, offering higher load capacity and greater durability than other structures.
- Misalignment Angle： The typical range for rod end bearings is 5° to 20°. Specialized two-piece rod ends can provide significantly larger angles.
- Application: Two-piece rod ends are widely used in demanding sports car racing applications. Examples include A-arms, control arms, trailing arms, radius rods, tie rods, drag rods, and track rods.
Three-Piece Rod End Bearings
The distinguishing feature of these rod ends is their superior ball-to-raceway contact. This design distributes the load over a greater surface area within the bearing.
- Features: Enhanced load distribution significantly improves durability, making them particularly effective in high-speed cycling environments. While they offer excellent life, their bodies can be slightly wider, which can result in slightly less misalignment than some two-piece designs.
- Material: The housing can be made of zinc-plated 4130 chrome-molybdenum steel or carbon steel. The ball is typically 52100 bearing steel, and the raceways are typically made of alloy steel (PTFE lining is optional). Lightweight options include 7075-T6 aircraft aluminum housings (typically red or black anodized), some with oil-impregnated sintered bronze raceways.
- Load capacity: Designed for heavy-duty and multi-functional applications. The maximum static axial load capacity for three-piece rod ends is generally recommended to be 10% of the ultimate static radial load capacity. Certain models, such as the JMX/JFX series, exhibit impressive static radial load capacities, ranging from approximately 2,800 lbs to over 100,000 lbs.
- Misalignment Angle： For example, the misalignment angle range of the JMX/JFX series is 7° to 17°.
- Application: It is commonly used in racing systems due to its enhanced durability, such as in shift linkages, suspension links, anti-roll bars, control arms, four-link systems, and tie rods.
By Thread Type
Threads are usually divided into external threads (male) and internal threads (female), while the length of the thread can be full thread or half thread.
Externally Threaded (Male) Rod End Bearings
These rod ends have a threaded shank with a protruding external thread. They are designed to screw into internally threaded components or connecting rods. This design provides a strong connection and allows for adjustment during assembly.
Application: For example, automotive suspension systems, steering linkages, and connection points in various industrial machinery.
Internally Threaded (Female) Rod Ends
In contrast to male rod ends, these rod ends have threads on the inside. They are designed to accept rods or studs with external threads. This design can provide a more compact connection or greater installation flexibility in certain applications.
Application： Commonly used in hydraulic cylinder connections, control rods, and various mechanical transmission devices.
Common metric and imperial rod end bearing thread sizes
Thread type | Thread size | Typical Thread Pitch (mm or TPI) |
Metric (M) | M3 | 0.5 |
| M4 | 0.7 |
| M5 | 0.8 |
| M6 | 1 |
| M8 | 1.25 |
| M10 | 1.5 |
| M12 | 1.75 |
| M16 | 2 |
| M20 | 2.5 |
| M24 x 2 | 2 |
| M30 x 2 | 2 |
| M36 x 2 | 2 |
| M42 x 2 | 2 |
Inch | 1/4″-28 | 28 |
| 3/8″-16 | 16 |
| 1/2″-13 | 13 |
| 5/8″-18 | 18 |
| 5/8″-11 | 11 |
| 3/4″-16 | 16 |
| 3/4″-10 | 10 |
| 7/8″-9 | 9 |
| 1″-8 | 8 |
By Material
The rod end material you choose will affect its strength, weight, or rust resistance.
Housing Material
- Carbon Steel: An economical and widely used material. Often an economical choice for medium-duty applications. Often silver or yellow zinc plated for enhanced corrosion resistance.
- Alloy steel (e.g., 4130 chrome-molybdenum steel, 4340): Known for its exceptional strength, alloy steel is often heat-treated to further enhance its properties, making it an excellent choice for high-load or demanding racing applications. It can also be coated with black oxide for additional surface protection.
- Stainless steel (e.g., 304, 440C, 17-4PH, 15-5PH, PH13-8Mo): Its excellent corrosion resistance makes it an indispensable choice for harsh environments such as food processing, marine applications, or outdoor installations, where exposure to moisture and corrosive substances is a constant.
- Aluminum (e.g., 7075-T6 aviation aluminum): Selected for its lightweight properties, aluminum is an ideal choice for weight-sensitive applications, particularly in motorsports, where minimizing mass directly impacts system dynamics and performance. It is often anodized to provide a durable, colored surface finish and enhance surface hardness.
- QT steel (quenched and tempered steel): This material is used in larger housing sizes and offers rugged strength and improved toughness, making it suitable for heavy-duty industrial applications.
Sphere Material
- 52100 bearing steel: This is a very common, high-performance material. It is typically precision ground, heat-treated, and hard chrome plated for exceptional durability and superior wear resistance.
- Stainless steel (e.g., 440C) : Provides inherent corrosion resistance. Sometimes chrome plated to increase surface hardness and wear resistance.
Raceway/Lining Material
- Brass: This material provides good lubricity, precise clearance control, excellent wear resistance, and efficient load distribution.
- Polytetrafluoroethylene (PTFE): A high-performance, self-lubricating lining material. It significantly reduces friction and eliminates the need for external maintenance. Often used with brass mesh for added structural integrity.
- Bronze: Commonly found in lubricated rod end bearings, the bronze raceway is often split into two sections to accommodate an oil groove for lubrication. Sintered bronze, an oil-impregnated porous material, is also used in some designs for maintenance-free operation.
- Nylon/Engineering Thermoplastics: Used for self-lubricating raceways, they help reduce maintenance requirements. They can be injection molded and reinforced with PTFE for improved performance. However, it should be noted that while nylon raceways may offer higher static radial load capacity, this comes at the expense of stiffness, and they tend to break into multiple pieces upon failure.
Here are some tips for choosing rod ends:
Factor | Key considerations | Impact on performance |
Loads (static and dynamic) | Tensile/compression/alternating loads, impact loads, load direction changes | Durability, service life, noise, potential for permanent deformation (Brinell indentation) |
Type of exercise | Rotational motion, oscillation angle, low-amplitude alternating motion | Smoothness, friction, service life, noise/vibration |
Operating Environment | Dust/contaminants, corrosive/humid environments, chemical exposure | Wear, corrosion, reliability, lifespan |
Temperature range | Min./max. operating temperature, coefficient of thermal expansion | Material properties, lubricant effectiveness, load capacity |
Misalignment angle | Required articulation angle, installation error, structural deformation | Stress concentration, system flexibility, wear, smooth operation |
Maintenance requirements | Lubrication accessibility, regular maintenance capabilities | Downtime, operating costs, lifespan, reliability |
Material selection | Strength, weight, corrosion resistance, wear resistance | Load capacity, lifespan, environmental adaptability, cost |
Cost-effectiveness | Initial cost, maintenance costs, life expectancy, performance requirements | Total cost of ownership, return on investment |
Despite their compact size, rod ends play a vital role in countless mechanical systems, ensuring smooth, flexible, and reliable operation. With over 20 years of experience manufacturing stainless steel rod ends, Profab offers a wide variety of rod ends. With state-of-the-art CNC machining centers and professional staff, we look forward to collaborating with you.
FAQ
What are the common causes of rod end bearing failure? How can they be prevented?
Common causes of failure include:
- Insufficient lubrication: This is the leading cause of failure and can lead to increased friction, excessive wear, and seizure.
- pollute: Dust, dirt, water, or metal particles can damage the bearing lining and accelerate wear.
- Overload: Exceeding design limits can result in permanent deformation or surface fatigue.
- Assembly Error: Improper installation or torque may cause premature failure.
- Prevention: Regular inspection, proper lubrication, cleanliness, proper installation (follow manufacturer’s instructions and use a torque wrench), protection of seals/dust boots, and prompt replacement of worn parts.
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