What is common between ball bearings and solid bearings?

Both ball bearings and solid bearings typically require some form of lubricant to function effectively. Lubrication reduces friction between moving parts, which is crucial in maintaining the operational efficiency of both types of bearings. In ball bearings, the lubricant helps the balls roll smoothly between the races, while in solid bearings, lubrication aids in minimizing wear and ensuring that the surfaces glide over one another effectively. Proper lubrication not only enhances performance but also extends the lifespan of the bearings by preventing overheating and reducing wear.

While the other options touch on aspects of bearing maintenance and requirements, they do not universally apply to both types of bearings in the same way that lubrication does. For instance, while some bearings may not require sleeves, lubrication is a foundational necessity for ensuring that both designs operate smoothly and effectively.