Which type of rolling element bearing uses balls to maintain the separation between the bearing races?

• A. Ball bearings
• B. Roller bearings
• C. Flat key
• D. Woodruff key

Answer: (A)

Rolling element bearings reduce friction by letting rolling elements ride between the inner and outer races, maintaining a precise gap while carrying load. When those rolling elements are spheres, the bearing type is a ball bearing. The balls roll as the shaft turns, distributing load through many small contact points, which lowers friction and enables smooth rotation at higher speeds.

Roller bearings use cylindrical or tapered rollers instead of balls, which changes how load is carried and how contact is distributed. The flat key and Woodruff key aren’t bearings at all; they’re used to lock components to a shaft and don’t provide the rolling separation between races.