What type of bearing contains many small diameter cylindrical rollers that ride directly on the shaft?

The correct choice is a needle bearing. Needle bearings are designed to accommodate a shaft and contain many small diameter cylindrical rollers, which allows them to provide a large load-bearing surface while maintaining a compact size. The design of needle bearings enables them to support radial loads effectively due to the reduced diameter of the rollers, which minimizes friction and enhances performance in applications where space is limited.

In contrast, ball bearings use spherical balls that can more effectively handle both radial and axial loads but are generally bulkier in comparison. Journal bearings and sleeve bearings are types of plain bearings that rely on a sliding surface rather than rolling elements; they do not contain rollers of any kind, which distinguishes their functionality from that of needle bearings. Therefore, the unique structure and function of needle bearings make them the fitting answer to this question.