Which is NOT one of the six general classifications of bearings?

• A. Ball Bearings
• B. Cylindrical Roller Bearings
• C. Needle Bearings
• D. Plain Bearings

Answer: (D)

The key idea is that bearings are grouped by design into rolling-element types, which is what the six general classifications cover, while plain bearings are a separate category. The six rolling-element classifications include ball bearings, cylindrical roller bearings, needle bearings, spherical roller bearings, thrust ball bearings, and thrust roller bearings. Plain bearings, on the other hand, are sliding-contact bearings where a shaft moves within a bushing or sleeve, separated by a lubricant film rather than by rolling elements. Because they rely on sliding motion rather than rolling elements, they aren’t included in the six rolling-element classifications. So, plain bearings are a different category, often referred to as journal or sleeve bearings, and are not part of the six rolling-element types.