Support movement and transmit loads.

A bearing constrains movement in some directions while allowing the intended motion. Shaft bearings transfer loads into a housing while allowing rotation.

Bearings are found in motors, sheaves and gearboxes. They help maintain alignment as well as reducing resistance to motion.

Inside a typical rolling bearing.

Look into the end of the shaft.

End-on cutaway through a ball bearing around a shaftOuter and inner rings form two raceways. Eight balls roll between them. An orange cage separates the balls. The shaft sits within the inner ring. The near seal and parts of the cage are omitted to expose the components.12345
  1. Outer ring and its raceway. The inward-facing track contacts the balls and transfers load to the housing.
  2. Inner ring and its raceway. The outward-facing track contacts the balls; the ring fits around the shaft.
  3. Rolling elements. Balls in this example roll between the two tracks; other bearings use rollers.
  4. Cage. Keeps the rolling elements apart. Its pockets are simplified here.
  5. Shaft. Its load passes through the inner ring, rolling elements and outer ring to the housing.

Now look at the shaft from the side.

Side view of a shaft and bearing with radial and axial loadsThe shaft axis runs horizontally through the bearing. A downward radial-load arrow is perpendicular to that axis. A rightward axial-load arrow lies along the shaft axis. These arrows represent possible force directions, not movement.12
  1. Radial load. Acts across the shaft, at right angles to its axis (the dashed line).
  2. Axial or thrust load. Acts along the shaft’s axis. A real installation may combine both directions.
Simplified bearing views, with covers omitted in the cutaway. Load direction is separate from bearing suitability: capacity depends on the bearing type, size, arrangement and duty.

Rolling contact usually reduces resistance compared with an equivalent sliding support, but it is not friction-free. Contact deformation, sliding, lubricant and seals all contribute to losses.

Radial and axial describe load direction.

A radial load acts across the shaft, perpendicular to its axis. An axial or thrust load acts along the shaft. Some applications impose both.

Different bearing designs carry different combinations of load. Physical size alone does not determine whether a bearing suits the duty.

Not every bearing contains balls.

A shaft turning in a bush

A plain bearing supports motion through a sliding interface. Its materials and lubrication arrangement are selected for the load, speed and environment.

Plain and rolling bearings are alternative approaches, not a simple good-versus-bad choice. Some plain bearings use self-lubricating materials; others rely on a supplied lubricant film.

Condition depends on the whole installation.

Load, alignment, contamination, lubrication and temperature affect service life. Damage can produce noise, vibration or increased resistance, but a noise alone does not identify its source.

An inspection considers the bearing alongside the shaft, housing and connected machinery. Replacement needs the correct specification, fit and installation method.

A closer look

A bearing arrangement must locate the shaft while allowing for effects such as thermal expansion where the design requires it. Excessive constraint or incorrect clearance can introduce loads that were not intended.

Check your understanding

Does “radial load” mean a force acting along the shaft?

Reveal the explanation

No. Radial load acts perpendicular to the shaft axis. Axial load acts along it.

Further reading.

Optional reading to explore this lesson in more detail.

  • NSK: bearing basics and components

    Start with the load-direction diagrams and the structure-and-components section. The cage animations show how rolling elements are spaced, making this a useful visual introduction.