Which of the following is an example of a rolling pair?

• A. Bolt and nut
• B. Lead screw of a lathe
• C. Ball and socket joint
• D. Ball bearing and roller bearing

Answer: (D)

A rolling pair is characterized by the relative motion of two elements where one rotates about the other with minimal friction. In the given options, the combination of ball bearing and roller bearing exemplifies this concept best.

Ball bearings and roller bearings are designed to facilitate rotational motion while minimizing friction between moving parts. They operate on the principle of rolling motion, where spherical or cylindrical elements (ball or roller) roll over each other, allowing for smooth rotation and efficient load distribution. This design contrasts with sliding pairs, where surfaces slide against each other, resulting in increased friction and wear.

In contrast, a bolt and nut represent a type of fastener which relies on sliding and static contact for tensioning rather than rolling. The lead screw of a lathe involves linear movement rather than a rotational rolling mechanism. Lastly, while a ball and socket joint does allow for rotational movement, it is primarily a biological joint where surfaces slide against each other rather than roll, making it less representative of the rolling pair concept compared to the interaction between ball bearings and roller bearings.