Sealed bearings generally require what regarding lubrication?

Sealed bearings are specifically designed to contain lubricants within their housing, which greatly reduces the need for any external lubrication maintenance. The sealing mechanism prevents contaminants from entering and keeps the lubricant from leaking out, thus providing a long service life without the need for constant reapplication of lubricant.

This design allows sealed bearings to operate effectively in various environments, as they come pre-lubricated with sufficient grease or oil that is meant to last the lifetime of the bearing under normal operating conditions. Consequently, it is not necessary to lubricate them frequently or at all during regular maintenance periods, hence the choice indicating that they require no lubrication is accurate.

In contrast, other bearing types might need regular, frequent or minimal lubrication, depending on their design and application, but sealed bearings are engineered specifically to eliminate these requirements.