Which of the following is required for a sealed ball bearing?

A sealed ball bearing is designed to operate without the need for constant lubrication under normal use, as the seal protects the lubricant inside from contamination and prevents it from escaping. This design minimizes maintenance requirements because the lubricant is contained within the bearing, allowing it to function smoothly over time without the need for frequent servicing.

In contrast, constant lubrication, or the requirement for cleaning and maintenance, does not apply to sealed bearings, as their sealed nature creates a maintenance-free environment under typical operational conditions. While certain greases may be specified for use with bearings to optimize performance, the key feature of sealed ball bearings is that they eliminate the necessity of regular lubrication, making them particularly advantageous for applications where maintenance access is challenging.