What are the different types of ball bearings?

1. Primary Classifications and Mechanical Design Principles

In the field of mechanical power transmission, the primary goal is to manage forces while facilitating movement. Ball bearings are the most common solution to this challenge. While they all share the common trait of using spheres as rolling elements, the internal architecture of these bearings varies significantly to handle different directions of force. To understand these types, we must first define the two types of loads: radial loads, which act perpendicular to the shaft, and axial loads, which act along the path of the shaft.

1.1 Deep Groove Ball Bearings (DGBB)

Deep groove ball bearings are the most prevalent type used in the global industry. Their design is characterized by raceway grooves on both the inner and outer rings that have circular arcs slightly larger than the radius of the balls.

Design and Functionality
The “deep” nature of these grooves allows the balls to remain seated even when subjected to high rotational speeds. This geometry creates a stable contact point that can manage radial forces exceptionally well. Furthermore, because the walls of the grooves are high, these bearings can also support a fair amount of axial thrust from either direction.

Key Advantages

• Low Frictional Torque: Because the contact area is relatively small, these bearings generate very little heat and friction. This makes them the first choice for energy-efficient electric motors.
• Ease of Use: They are non-separable, meaning the unit comes as a single piece that is easy to install.
• Quiet Operation: The high precision of the groove finish allows for near-silent operation, which is critical for consumer electronics and office equipment.

1.2 Angular Contact Ball Bearings

Angular contact ball bearings are designed for more complex mechanical environments where forces do not come from a single direction. The raceways of the inner and outer rings are displaced relative to each other along the bearing axis.

The Mechanics of the Contact Angle
The defining feature of this bearing is the contact angle. This is the angle between the line joining the contact points of the ball and the raceways in the radial plane. This design allows the bearing to support “combined loads,” which are simultaneous radial and axial forces.

Single Row vs. Double Row

• Single Row: These can only support axial loads in one direction. In most machinery, they are installed in pairs. When two bearings are mounted back-to-back, they create a rigid arrangement that can handle tilting moments.
• Double Row: This design incorporates two rows of balls in a single unit. It saves space and can handle axial loads from both directions without needing a second bearing.

1.3 Self-Aligning Ball Bearings

One of the greatest challenges in large-scale machinery is maintaining perfect alignment. When a long shaft rotates, it may bend or flex under its own weight or the weight of the load. Standard bearings would experience extreme stress and fail under these conditions.

Spherical Outer Raceway
The self-aligning ball bearing solves this through its unique outer ring. The inner surface of the outer ring is ground into a perfect sphere. This allows the inner ring, the cage, and the two rows of balls to swivel together.

Operational Benefits

• Compensation for Errors: It can handle a misalignment of several degrees without increasing friction or reducing service life.
• Cool Running: Even at high speeds, the dual-row design and the ability to tilt keep the bearing running cooler than many other types in similar conditions.

1.4 Thrust Ball Bearings

While most bearings are designed to handle forces coming from the side, thrust ball bearings are built to handle forces pushing directly against the end of the shaft.

The Sandwich Construction
A thrust ball bearing consists of two flat plates, often called washers. One is the shaft washer (attached to the rotating shaft), and the other is the housing washer (attached to the stationary base). The balls are held in a cage between these two plates.

Critical Limitations
It is vital to note that thrust ball bearings cannot handle any radial loads. If a side force is applied, the washers will shift, and the bearing will likely fall apart or jam. Because of this, they are often used in conjunction with a separate radial bearing that manages the side-to-side stability of the shaft.

Comparison of Design Features

The table below summarizes the design priorities of these four fundamental types.

2. Technical Performance and Comparative Analysis

In mechanical engineering, performance is measured by how effectively a component handles speed, load, and environmental stress. This chapter breaks down the operational characteristics of the primary ball bearing types to help determine which design is best suited for specific technical requirements.

2.1 Load Carrying Capacity

Load capacity is divided into two categories: static and dynamic. Dynamic load capacity refers to the stress a bearing can handle while rotating, while static capacity refers to the weight it can support while stationary without permanent deformation of the balls or raceways.

• Radial Dominance: Deep groove and self-aligning bearings are the primary choices when the weight is pushing down on the shaft. However, deep groove bearings offer much higher rigidity because of the tight conformity between the ball and the groove.
• Axial Superiority: Thrust ball bearings are the absolute leaders in pure axial load. However, for high-speed axial needs (like in a jet engine or a car’s transmission), angular contact bearings are superior because they maintain their geometric integrity under high centrifugal forces.

2.2 Speed Limits and Thermal Stability

Speed is the enemy of bearing life. As a bearing rotates faster, it generates heat due to the internal friction of the lubricant and the contact between the balls and the cage.

• High-Speed Leaders: Deep groove ball bearings are generally capable of the highest rotational speeds because they have the lowest friction profile.
• The Heat Factor: Angular contact bearings also perform well at high speeds, but they generate more heat than deep groove types because of the angled contact point. High-precision versions of these bearings often require specialized oil-mist lubrication to stay cool at speeds exceeding twenty thousand revolutions per minute.
• The Speed Limit of Thrust Bearings: Thrust bearings have the lowest speed ratings. If they spin too fast, centrifugal force pushes the balls toward the outer edge of the washers, leading to a phenomenon known as “smearing,” which destroys the raceway surface.

2.3 Precision and Running Accuracy

Running accuracy refers to how much the shaft “wobbles” or moves from its intended center during rotation.

• High Precision: Angular contact bearings are the gold standard for precision. Because they can be “preloaded” (pressed together during installation to remove all internal clearance), they provide an extremely rigid and stable rotation. This is why they are found in the spindles of computer-controlled milling machines.
• Standard Precision: Deep groove bearings provide excellent accuracy for general consumer goods but usually have a small amount of internal “play” or clearance to allow for thermal expansion.

Comparative Performance Table

The following data provides a high-level comparison of performance metrics based on standard engineering benchmarks.

2.4 Environmental and Geometric Constraints

The physical space available in a machine often dictates the bearing type regardless of the load.

• Spatial Efficiency: If the machine has very little radial space (the distance between the shaft and the outer housing), engineers might choose a thin-section deep groove bearing.
• Mounting Errors: In large industrial fans or agricultural equipment, the housing is rarely perfectly straight. In these environments, the performance of a deep groove bearing would drop by eighty percent, whereas a self-aligning bearing would continue to perform at its peak efficiency.

2.5 Summary of Selection Criteria

When choosing between these types, an engineer must ask three primary questions:

1. What is the primary direction of force? (Radial, Axial, or Both)
2. What is the required speed? (Low, Moderate, or Ultra-high)
3. How precise must the rotation be? (General utility vs. High-precision machining)

By analyzing the data in this chapter, it becomes clear that there is no “perfect” bearing, only the “correct” bearing for the specific environment.

3. Materials Science and Specialized Variations

While the mechanical design of a bearing dictates how it handles force, the materials used in its construction determine how it survives its environment. As industrial demands have evolved, engineers have moved beyond standard steel to develop specialized variations that can withstand extreme heat, corrosive chemicals, and even vacuum conditions.

3.1 Standard Chrome Steel (SAE 52100)

The vast majority of ball bearings are manufactured from high-carbon chrome steel. This material is chosen for its exceptional hardness and fatigue resistance. When heat-treated, it provides a tough surface that can withstand the constant rolling pressure of the balls without cracking or deforming.

• Strength: It has a high elastic limit, meaning it returns to its original shape after being compressed by a load.
• Weakness: Its primary drawback is a lack of natural corrosion resistance. Without a consistent film of oil or grease, chrome steel will oxidize and rust rapidly, especially in humid environments.

3.2 Stainless Steel Variations

In industries where hygiene or chemical resistance is mandatory, such as food processing or pharmaceutical manufacturing, stainless steel is the standard.

• AISI 440C: This is the most common stainless steel for bearings. It contains enough carbon to be hardened through heat treatment, maintaining a high load capacity while resisting rust.
• AISI 304 and 316: These grades offer even higher corrosion resistance (especially against saltwater and acids) but cannot be hardened to the same degree as 440C. Therefore, they are used for low-load applications where chemical survival is more important than mechanical strength.

3.3 Ceramic Hybrid Bearings

One of the most significant advancements in recent decades is the development of hybrid bearings. These utilize standard steel rings but replace the steel balls with ceramic spheres, typically made of Silicon Nitride.

• Weight and Centrifugal Force: Ceramic balls are approximately forty percent lighter than steel. At high speeds, thisweight reductiont significantly decreases the centrifugal force acting on the outer raceway, allowing the bearing to run much faster and cooler.
• Thermal Properties: Ceramics do not expand as much as steel when heated. This thermal stability prevents the bearing from “seizing” or locking up during high-temperature operations.
• Electrical Insulation: Unlike steel, ceramic is a non-conductive material. In modern electric motors and wind turbines, stray electrical currents can jump across a steel bearing, causing a type of damage called “pitting” or “fluting.” Ceramic balls act as an insulator, eliminating this risk.

3.4 Specialized Geometry: Thin Section and Miniature Bearings

Sometimes, the material is less important than the physical footprint of the bearing.

• Miniature Bearings: These are defined as bearings with an outer diameter of less than thirty millimeters. They are used in precision instruments like medical devices, small drones, and high-end computer fans. They require extreme manufacturing cleanrooms to ensure that even a microscopic speck of dust does not jam the rotation.
• Thin Section Bearings: In robotics and aerospace, engineers often face a dilemma: they need a large diameter shaft but have very little space for the bearing housing. Thin-section bearings maintain a consistent cross-section regardless of the bore size. This allows for hollow shafts that can carry wires or plumbing through the center of a robotic joint.

Comparison of Material Properties

The following table highlights the differences between the three most common material configurations used in modern ball bearings.

3.5 High-Performance Cages

The cage (or retainer) is the component that keeps the balls separated. While often overlooked, the cage material is vital for high-performance applications.

• Steel Cages: Strong and cost-effective for general use.
• Brass Cages: Used in heavy-duty applications where there is a lot of vibration or high acceleration. Brass is naturally “self-lubricating” and reduces friction against the balls.
• Polyamide (Plastic) Cages: These are lightweight and flexible. They are favored in high-speed applications because they generate less heat and can handle rapid changes in velocity.

4. Sealing Technology and Lubrication Strategies

The physical design and material of a ball bearing determine its potential, but the sealing and lubrication determine its actual lifespan. Statistics from the bearing industry suggest that over eighty percent of premature bearing failures are caused by improper lubrication or the ingress of contaminants like dust and moisture. This chapter explores how these “soft” components protect the “hard” steel of the bearing.

4.1 Shielding vs. Sealing

To protect the internal raceways and balls, manufacturers offer different levels of enclosure. These are generally classified into shields and seals.

Metal Shields (Z or ZZ)
Shields are typically made of stamped steel and are fixed to the outer ring, extending toward the inner ring without actually touching it.

• Advantages: Because there is no physical contact with the inner ring, there is no added friction. This allows shielded bearings to operate at the same maximum speeds as open bearings. They are excellent for keeping out large debris.
• Disadvantages: Since they do not form a tight seal, they cannot prevent the entry of fine dust or liquids, nor can they perfectly retain grease in vertical applications.

Rubber Seals (RS or 2RS)
Seals are made of synthetic rubber bonded to a steel insert. Unlike shields, the lip of the seal makes physical contact with the inner ring.

• Advantages: They provide a near-perfect barrier against moisture, steam, and fine particulates. They are the standard for outdoor equipment and wash-down environments.
• Disadvantages: The contact between the rubber and the rotating inner ring creates friction and heat. This reduces the maximum speed rating of the bearing compared to an open or shielded version.

4.2 Lubrication: Grease vs. Oil

Lubrication serves three purposes: reducing friction, dissipating heat, and preventing corrosion.

• Grease Lubrication: Grease is the most common lubricant because it is easy to contain within the bearing. It consists of a base oil held in a “thickener” (like a sponge). It is ideal for moderate speeds and is often used in “sealed for life” bearings that require no maintenance.
• Oil Lubrication: Oil is used in high-speed or high-temperature applications where grease would break down or create too much drag. In complex machinery, oil can be circulated through a cooling system, effectively carrying heat away from the bearing.

Comparison of Enclosure Types

The following table summarizes the trade-offs between different bearing protection methods.

4.3 Understanding Internal Clearance

A critical but invisible factor in bearing performance is internal clearance. This is the total distance that one bearing ring can be moved relative to the other.

• Thermal Expansion: As a bearing runs, it gets hot. Steel expands when heated. If a bearing had zero clearance when cold, it would become too tight and seize up once it reached operating temperature.
• Standard vs. C3 Clearance: Most bearings are manufactured with “Normal” clearance. However, for high-heat applications, engineers specify “C3” or “C4” clearance. These bearings feel “loose” when you pick them up, but they become perfectly snug once the machine reaches its high operating temperature.

4.4 Factors in Lubricant Failure

Even the best lubricant has a limited life. Environmental factors can accelerate its degradation:

1. High Temperature: For every fifteen degrees Celsius increase in temperature, the life of the grease is roughly cut in half.
2. Water Contamination: Even a small amount of water (less than one percent) mixed into the grease can reduce the bearing life by over seventy percent.
3. Vibration: Excessive vibration can cause the oil to separate from the grease thickener, leaving the bearing dry.

Summary of Maintenance Prevention

In modern “Precision Maintenance” programs, the goal is to keep the lubricant clean, cool, and contained. By selecting the correct seal (like a 2RS for a dusty farm environment) and the correct clearance (like C3 for a high-speed motor), the service life of a ball bearing can be extended from months to years.

5. Industrial Applications and Failure Analysis

The final stage in mastering ball bearing technology is understanding how these components behave in the real world. By examining specific industrial case studies and analyzing the common causes of failure, engineers can bridge the gap between theoretical design and practical reliability.

5.1 Industrial Case Studies

Different sectors prioritize different bearing attributes based on their unique operational challenges.

Automotive Industry: The Hub Unit
In modern vehicles, the wheel hub uses specialized double-row angular contact ball bearings.

• The Challenge: The bearing must support the weight of the car (radial load) while resisting the massive side forces (axial load) generated during cornering.
• The Solution: By using a pre-adjusted double-row design, manufacturers ensure the wheel remains perfectly rigid, providing safety and precise steering response for the life of the vehicle.

Aerospace: Jet Engine Mainshafts
Jet engines require bearings that can survive speeds exceeding thirty thousand revolutions per minute and temperatures that would melt standard lubricants.

• The Challenge: High centrifugal force and extreme thermal expansion.
• The Solution: These engines often utilize ceramic hybrid bearings with silver-plated cages. The silver acts as a dry, “emergency” lubricant if the primary oil system fails, while the ceramic balls ensure the bearing does not seize under intense heat.

Medical Technology: High-Speed Dental Drills
A dental drill is one of the highest-speed applications in the world, often reaching four hundred thousand revolutions per minute.

• The Challenge: Extreme speed and the need for frequent sterilization in high-pressure steam (autoclave).
• The Solution: Miniature ceramic ball bearings are used because they are lightweight enough to handle the speed and resistant enough to survive the corrosive environment of a sterilization chamber.

5.2 Analyzing Why Bearings Fail

Despite the precision of their manufacture, bearings eventually reach the end of their fatigue life. However, most fail prematurely due to external factors. The study of these failures is known as “Root Cause Analysis.”

1. Fatigue and Flaking
This is the natural end of a bearing’s life. After millions of rotations, the metal surface begins to crack and “flake” away. If this happens early, it is usually a sign that the bearing was overloaded.

2. Brinelling (Indentation)
This occurs when a bearing is subjected to a massive shock load while stationary, such as hitting a machine with a hammer during installation. The balls are pushed so hard into the raceway that they leave permanent “dents.” This causes the bearing to vibrate and grow louder over time.

3. Electrical Erosion (Pitting)
Common in motors controlled by variable frequency drives, electricity can arc from the inner ring, through the balls, to the outer ring. Each spark melts a tiny amount of metal, creating a “washboard” pattern on the raceway. This is a primary reason for switching to ceramic hybrid bearings.

4. Contamination
If dust or sand enters the bearing, it acts as a grinding paste. The once-smooth balls become dull and undersized, leading to excessive play and eventual total failure of the machine.

Summary of Failure Modes

The following table serves as a diagnostic tool for identifying bearing issues in the field.

5.3 The Future: Smart Bearings and Industry 4.0

As we move toward a more connected industrial world, bearings are becoming “smart.” Modern high-end bearings can now be equipped with embedded sensors that monitor temperature, vibration, and rotation speed in real time. This data is sent to a central computer that can predict exactly when a bearing will fail, allowing companies to replace the part during scheduled downtime rather than suffering an expensive, unexpected breakdown.

Conclusion

From the simple deep groove design to the complex ceramic hybrid, ball bearings are a testament to human engineering. They are the essential interface between stationary and moving parts. By selecting the correct type, material, and sealing method, and by understanding the signs of potential failure, we ensure that the machines of the world continue to turn with efficiency and reliability.

6. Precision Selection and Installation Best Practices

The final transition from engineering theory to operational reality occurs during the selection and installation process. Even the highest-quality bearing will fail within hours if it is misapplied or installed with incorrect techniques. This chapter outlines the rigorous steps required to ensure that a bearing reaches its full calculated life expectancy.

6.1 The Selection Flowchart

When an engineer selects a bearing, they follow a logical hierarchy of needs. This process ensures that the most critical constraints are met first.

1. Space Constraints: The shaft diameter determines the bore of the bearing. If radial space is limited, thin-section bearings are chosen.
2. Load Magnitude and Direction: If the load is purely radial, deep groove bearings are the priority. If there is a heavy pushing force along the shaft, angular contact or thrust bearings are selected.
3. Speed Requirements: For ultra-high-speed applications, the friction profile of the bearing and the weight of the rolling elements (steel vs. ceramic) become the deciding factors.
4. Accuracy and Rigidity: Machines requiring extreme precision, such as robotic arms or optical grinders, necessitate bearings with high stiffness and minimal internal play.

6.2 The Importance of Fits and Tolerances

A bearing does not simply “sit” on a shaft; it must be held with the correct amount of pressure. This is known as the “fit.”

• Interference Fit (Tight Fit): Typically used for the ring that rotates. If the inner ring rotates, it must be pressed onto the shaft tightly so that it does not “creep” or slip, which would cause friction and wear on the shaft itself.
• Clearance Fit (Loose Fit): Typically used for the stationary ring. This allows for slight movement to accommodate thermal expansion as the bearing heats up during operation.

If a fit is too tight, it will remove the internal clearance of the bearing, causing it to overheat immediately. If it is too loose, the bearing will vibrate, leading to noise and mechanical damage.

6.3 Professional Installation Techniques

Improper installation is responsible for a large percentage of “infant mortality” in bearings (failures that happen shortly after start-up).

The Golden Rule of Mounting
Never apply mounting force through the rolling elements. If you are pressing a bearing onto a shaft, the pressure must be applied only to the inner ring. If you press on the outer ring to get the inner ring onto the shaft, the force travels through the balls, causing microscopic dents known as brinelling.

Thermal Mounting Methods
For larger bearings, mechanical force is often insufficient.

• Induction Heating: This is the preferred modern method. The bearing is heated electronically, causing the inner ring to expand. It is then slipped onto the shaft, where it shrinks to a tight fit as it cools.
• Cold Mounting: In some high-precision aerospace applications, the shaft is cooled using liquid nitrogen while the bearing remains at room temperature, allowing for a seamless fit.

6.4 Summary Table: Maintenance Dos and Don’ts

Final Synthesis: The Systemic View

Throughout this guide, we have traveled from the basic geometry of deep grooves to the molecular advantages of ceramics and the practicalities of industrial maintenance. A ball bearing is not a standalone commodity; it is a precision-engineered system. Its success depends on the harmony between its design, its material, its environment, and the human hands that install it.

As the global industry moves toward more sustainable and energy-efficient goals, the role of the ball bearing becomes even more vital. By reducing friction, we reduce energy consumption. By extending bearing life, we reduce material waste. Understanding the different types of ball bearings is, therefore, not just a technical necessity but a contribution to the efficiency of our modern world.

7. Future Trends in Ball Bearing Technology

As we look toward the next generation of mechanical systems, ball bearing technology is transforming. The push for carbon neutrality, the rise of electric mobility, and the digital revolution are driving innovations that go beyond traditional steel and grease. This final chapter explores the cutting-edge developments that will define the future of rotational motion.

7.1 Bearings for the Electric Vehicle (EV) Revolution

The transition from internal combustion engines to electric motors has created entirely new requirements for ball bearings. Electric motors operate at significantly higher speeds (often exceeding twenty thousand revolutions per minute) and require components that can handle rapid acceleration.

• High-Speed Stability: Future ball bearings are utilizing specialized carbon-fiber reinforced cages that are lighter and stronger than traditional brass or steel. This allows for the extreme RPMs required by modern EV drivetrains.
• Preventing Electrical Discharge: As discussed in previous chapters, electric motors can generate stray currents. Future standards are moving toward the universal adoption of ceramic balls or specialized non-conductive coatings on the outer rings to protect vehicle drivelines from electrical erosion.

7.2 The Rise of Smart Bearings (Industry 4.0)

In the era of the Industrial Internet of Things, the “dumb” bearing is becoming a thing of the past. Smart bearings are now being manufactured with integrated sensors that communicate directly with a factory’s central nervous system.

• Real-Time Condition Monitoring: These sensors measure vibration, temperature, and acoustic emissions. Instead of replacing a bearing based on a calendar schedule, companies can now wait until the sensor detects the very first signs of molecular fatigue.
• Autonomous Lubrication: Some advanced systems now feature bearings that can trigger their own lubrication cycles. When a sensor detects an increase in friction-induced heat, it signals an automated pump to deliver a precise milligram of oil, ensuring optimal conditions at all times.

7.3 Sustainability and Green Manufacturing

The bearing industry is increasingly focused on reducing its environmental footprint. This involves both the manufacturing process and the operational efficiency of the product.

• Reduced Rolling Resistance: New raceway grinding techniques are creating surfaces that are smooth at a near-atomic level. This reduces energy loss in machines, contributing to lower global electricity consumption.
• Biodegradable Lubricants: Research is currently focused on high-performance lubricants derived from plant-based esters rather than petroleum. These “green” greases are designed to offer the same protection as synthetic oils but with a significantly lower environmental impact in the event of a leak.

Comparative Analysis of Future Technologies

The following table summarizes the emerging technologies and their expected impact on industrial performance.

7.4 Specialized Surface Coatings

Beyond material changes, the future of ball bearings lies in surface “functionalization.” Using methods like Physical Vapor Deposition, manufacturers can apply coatings that are only a few microns thick but provide incredible benefits.

• Diamond-Like Carbon (DLC) Coatings: This coating provides a surface hardness approaching that of a diamond. It allows bearings to operate in “marginal lubrication” conditions where oil or grease may be temporarily absent.
• Anti-Corrosion Nanocoatings: These provide a barrier that is far superior to traditional stainless steel, allowing bearings to operate in highly acidic or saline environments without degrading.

7.5 Final Perspectives

The humble ball bearing remains one of the most significant inventions in human history. As we have seen throughout this comprehensive guide, the different types of ball bearings—from Deep Groove to Angular Contact and beyond—each play a specific role in supporting the infrastructure of our lives.

As technology advances, the focus will shift from simply “supporting a load” to “providing data and saving energy.” However, the fundamental principle will remain the same: the efficient management of motion through precision engineering. By understanding these components today, we are better prepared for the mechanical challenges of tomorrow.

Frequently Asked Questions (FAQ)

1. What is the most significant difference between a shield and a seal?
The primary difference lies in physical contact. A shield is a non-contact metal plate that protects the bearing from large debris while maintaining high-speed capabilities and low friction. A seal is a contact component, usually made of rubber, that touches the inner ring to provide a superior barrier against fine dust and liquids, though it increases friction and lowers the maximum speed limit.

2. When should I choose a ceramic hybrid bearing over a standard steel bearing?
You should opt for ceramic hybrid bearings in three specific scenarios: first, in ultra-high-speed applications where the lighter weight of ceramic balls reduces centrifugal force; second, in environments prone to electrical arcing (like electric motors) because ceramic is an insulator; and third, in high-temperature settings where thermal expansion must be minimized.

3. Why can a thrust ball bearing not support radial loads?
Thrust ball bearings are designed with a horizontal sandwich construction, featuring two parallel washers. Because the raceways are flat and oriented to handle vertical or axial pressure, any side (radial) force will cause the washers to slide across one another, potentially causing the balls to pop out of the tracks and leading to immediate mechanical failure.

4. What does a C3 or C4 clearance rating mean on a bearing?
These ratings indicate that the bearing was manufactured with more internal “play” or room between the balls and the raceways than a standard bearing. This extra space is intentional; it allows the components to expand as they get hot during operation without the bearing becoming too tight or seizing up.

5. How does a self-aligning ball bearing correct for a crooked shaft?
The secret is in the outer ring. The internal surface of the outer ring is ground into a continuous spherical shape. This allows the inner ring and the ball assembly to pivot or tilt freely within the outer ring, much like a ball-and-socket joint, while still maintaining smooth rotation.

Technical References

• ISO 15:2017 – Rolling bearings — Radial bearings — Boundary dimensions, general plan.
• ISO 281:2007 – Rolling bearings — Dynamic load ratings and rating life.
• ISO 76:2006 – Rolling bearings — Static load ratings.
• ANSI/ABMA Std. 9 – Load Ratings and Fatigue Life for Ball Bearings.
• DIN 625 – Rolling bearings — Single row deep groove ball bearings.
• Brändlein, J., Eschmann, P., Hasbargen, L., & Weigand, K. (1999). Ball and Roller Bearings: Theory, Design and Application (3rd ed.). Wiley.
• Harris, T. A., & Kotzalas, M. N. (2006). Essential Concepts of Bearing Technology. CRC Press.
• Hamrock, B. J., & Dowson, D. (1981). Ball Bearing Lubrication: The Elastohydrodynamics of Elliptical Contacts. Wiley.
• SKF Group. (2023). Rolling Bearings Catalogue.
• Timken Company. (2024). Engineering Manual: Metals Industry Edition.
• NSK Ltd. (2022). Motion & Control Technical Journal.
• Bearing World Journal. (Springer Nature).