AS9120B, ISO 9001:2015, and FAA AC 0056B ACCREDITED

Ball Bearing Design and Function

Ball bearings are a type of bearing that relies on the free motion of rolling balls to transfer and “bear” a load. By using rotating balls in place of gears or rollers, there is often less friction as a result of there being more free movement of present rolling elements. They are commonly used in engine shafts, centrifugal pumps, locomotive axles, and computer hardware where very small versions facilitate the rotation of internal fans. While there are a variety of different ball bearing types, most of them consist of three basic parts which are the balls, races, and cage.

Design of Ball Bearings

Regardless of their type, all ball bearings are defined by their usage of multiple balls, with some containing hundreds, while others may only require three or four. The main purpose of the balls is to transmit a load so that when they are exposed to significant force, the balls will rotate to reduce friction. Additionally, these balls work in conjunction with a pair of races or “pathways” which the balls move along. To best contain them, most designs feature an inner and outer race that have a uniform groove in the center. As the balls rotate, they will follow this groove and remain confined in the bearing, even when they are not fully enclosed. Finally, the part of a ball bearing between the inner and outer races is called the cage. Acting as a container for the balls, the cage keeps the balls separated while they roll and holds them within the bearing body without restricting their rotation. Without a cage, the balls can easily wear out or become stuck.

Materials Used in Ball Bearings

The materials used to make ball bearings vary widely in accordance with their application. In addition to finding the right material for each part, it is important to make sure that the different materials used will work well with each other, as they will be in close contact. Hardened steel is one of the most common materials used for the balls employed in these bearings. As a highly durable and corrosion resistant metal, hardened steel holds up well amid continuous operation. Alternatively, there is stainless steel which is most often used for ball bearings made of plastic. Still durable, but with a lower price and hardness, stainless steel is less likely to damage the plastic components while remaining corrosion resistant against saltwater and alkalis.

Where metal-free ball bearings are needed, glass balls are often favored for their high chemical resistance and smoothness. Soda-lime glass in particular is used to make bottles, drinking glasses, and many ball bearings, but should never be used for areas of great chemical stress. For these circumstances, borosilicate glass can be used as it has greater chemical resistance, even finding use in applications that involve strong acids. Finally, there are balls made of ceramic, either in the form of aluminum oxide or silicon nitride. Aluminum oxide ceramic is known for being lightweight and having good resistance to corrosion, abrasion, and heat. However, it should never come in contact with hydrochloric acid, hydrofluoric acid, strong alkaline solutions, or warm sulphuric acid. Silicon Nitride is similarly lightweight, but has greater toughness and corrosion resistance.

Ball Bearing Specifications

With a plethora of ball bearing types available on the market, most options are classified and organized by their dimensions and operating specifications. The first dimension to consider is the bore or the inner diameter of the bearing which encapsulates the central hole wherein the balls roll. If the bore is a hexagonal hole, this measurement will refer to the dimension across the flats, and if the bearing is tapered or conical, this will be referring to the smaller diameter. Another dimension to consider is the outside diameter, which includes the housing (for housed units), but not the flange (for flanged bearings). The width of the outer race represents the total width of the outer diameter of the bearing. Lastly, there is the overall width which includes a locking collar if it is present.

Whereas dimensions refer to the physical shape of the bearing, its operating specifications refer to the device’s capabilities. The rated speed is a measurement of the greatest rpm a ball bearing can safely operate at. For some bearings, this might refer to the speed that it can reach alongside the use of grease or oil and will be specified as such. Another operating specification is the dynamic thrust or axial load which is the measure of how much axial thrust the bearing is built to handle. Conversely, there is the dynamic radial load measurement which refers to the opposite.

The Function of Ball Bearings

The main role for ball bearings is to reduce rotational friction, as well as support axial and radial loads. They can do this by using two races and a set of balls that can transmit a load via rotational movement along a pathway. Typically, the races will consist of one stationary pathway, along with a moveable one. During the rotation of one of the bearing races, the balls also rotate, transferring motion and force from one racing to another. The load capacity of ball bearings tend to be lower than other types of rolling-element bearings because of the smaller contact between the races and balls. However, the balls exhibit very low friction and can tolerate some misalignment of both the inner and outer races.

Applications for Ball Bearings

There are many possible applications for bearings within the aerospace, automotive, agricultural, medical, military, and consumer goods sectors, among other specialty projects. Within the aerospace and aviation sector, in particular, ball bearings are frequently employed in air circulation systems, fuel supply machinery, navigation tools, airframe components, and many other crucial equipment. Like any aviation- or aerospace-grade part, the bearings used on aircraft must be resistant to vibration, temperature and pressure changes, and more, to be evaluated as airworthy.


When your assembly requires high-grade bearings of proven durability and airworthiness, Aircraft Parts Supplier has you covered with our inventory of products. Sourcing only from top manufacturers who adhere to a high standard of quality assurance in their operations, we proudly stand behind the dependability of our offerings. Within the Aviation Parts section of our website, you can find a page of all the aircraft bearings we currently have available for purchase. There, we invite you to explore our offerings and freely request quotes for your comparisons on any items of interest. Backed by a widespread supply network and unique market expertise, we guarantee solutions fit to your exact needs, wherever you are located!


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