Which of the following is NOT a common type of bearing?

The choice identifying ratchet bearing as not a common type of bearing is accurate because ratchet bearings are not typically classified alongside the well-known bearing types used in power transmission.

Ball bearings, roller bearings, and sleeve bearings are established and widely employed in various mechanical applications. Ball bearings utilize spherical balls to maintain separation between the moving parts, allowing for smooth rotation and reducing friction. Roller bearings, on the other hand, employ cylindrical rollers and are designed to handle higher loads compared to ball bearings. Sleeve bearings, also known as plain bearings, do not use rolling elements; they rely on a sliding motion between the shaft and the bearing surface to reduce friction.

In contrast, while a ratchet mechanism may be used in some applications for transmitting rotational movement—allowing motion in one direction and preventing it in the opposite direction—it does not fit into the primary categories of bearings typically encountered in millwright and mechanical contexts.