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In this issue of NPB’s e-News we are presenting an article on a specific design feature of industrial spherical bearings. This article introduces the common feature of cracked races from both the assembly and application perspective.

Article by Scott Rinne, NPB Industrial Product Manager

From time to time our sales and product group take calls from new users of spherical plain bearings who are concerned about cracks in the outer ring of the bearings they’ve received. Spherical plain bearings (sometimes known as ball bushings or fractured race spherical bearings) all have a split outer ring as a common design feature. To the casual observer this may appear to be a flaw in the part but in reality this feature provides for unique advantages in the spherical plain bearing’s value and application.

The outer ring is fractured, typically in one place to accommodate assembly of the ball and ring.  Due to the strength and hardness of the metal the fracture is necessary to allow for installation of the ball into the raceway.  When larger bearings are manufactured two fractures or cuts are made, in turn creating a three piece bearing. The fractures are generally created by grinding a V shaped notch into the outer ring and then applying a large amount of force over that notch to make a precise break.

Bearing Assembly

There are two different types of spherical plain bearings; radial and angular contact. Radial bearings include an outer ring with a concave spherical surface.  The outside diameter of the inner ring, or ball, has a convex spherical surface. These two spherical diameters are then matched to offer the optimum combination of load capacity and bearing frictional torque. This attention to detail in both design and manufacturing makes NPB spherical plain bearings products of choice, best suited for applications requiring the transmissions of heavy loads under oscillatory as well as continuous rotational motions. They are also intended for applications requiring angular misalignment. Our bearing rings and balls are made of high strength bearing steel, heat treated to Hrc 58 minimum hardness for longevity and performance.

Radial Spherical Plain Bearing

Angular contact bearings are best suited for applications with single direction, thrust load. When thrust load reverses, angular contact bearings will separate. Therefore, for applications with reversing thrust load, it is necessary to use a pair of angular contact bearings. For applications requiring moment flexibility, arrange angular contact bearings in Face-to-Face or "DF". For applications requiring high moment rigidity, arrange angular contact bearing in Back-to-Back or "DB".

Angular Contact Spherical

Spherical plain bearings are available in multiple configurations.  Standard designs include inch and metric options with either a metal on metal configuration or with a PTFE, self lubricating raceway.  Extended inner raceways are also available as well as heavy duty parts for the most severe requirements.


Used for low speed applications where misalignment is necessary, common uses for spherical plain bearings include;

  • Hydraulic cylinders
  • Steering Axles on heavy machinery
  • Hinge Pin on large hauling trucks
  • Tilt Cylinder on forklifts
  • Articulating Joint on front end loaders

NPB manufactures and inventories a complete line of spherical plain bearings as well as many special designs created for specific customer focused solutions. Whether you need a standard replacement part, or help with a difficult design problem you can rely on NPB for continuous assistance.  When you work with NPB not only do you get access to our inventory, you gain the support of our experienced sales staff as well as a wide vendor knowledge base.  Additional services such as our ISO 9001:2000 relubrication facility make NPB a valuable supply solution for a wide range of requirements. 

Contact your local NPB sales rep today or visit for more information. 

NPB stocks a broad range of Spherical Plain Bearings including a full line of inch sizes, metric standards, angular contact, extended inner ring, heavy duty, and self-lubricating. To use our product selection tool please visit our Spherical Plain Bearing page. Please visit our Part Interchange to find an interchange to NPB part numbers from other manufacturers’ part numbers.

Spherical Plain Race Load Bearings

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