What characteristic is associated with mechanical joints?

Mechanical joints are designed to allow for some movement between connected parts while maintaining a stable connection. This characteristic enables flexibility, accommodating expansion, contraction, and other dynamic forces that may occur during operation. Mechanical joints can often absorb vibrations and misalignments due to their inherent design, which is critical in applications requiring durability and resilience under varying operational conditions.

The other options do not accurately reflect the primary function of mechanical joints. For instance, the notion that they are not flexible contradicts their purpose of allowing movement. Similarly, suggesting that they provide a rigid connection ignores the flexibility aspect, as some mechanical joints can indeed pivot or shift. Lastly, stating that they are always used underwater is overly specific and not representative of their broader applications across various environments.