Which icon activates the Smart Dimension tool to add dimensions to a sketch?

The icon that activates the Smart Dimension tool to add dimensions to a sketch is represented by two parallel lines. This icon is an intuitive representation of the function, as it suggests the relationship of dimensions between two entities or features, analogous to how dimensions relate to parallel lines in a sketch.

When you select this icon, it allows you to click on any sketch entity, such as lines, arcs, or circles, to define their dimensions accurately. The Smart Dimension tool automates the process of setting the appropriate dimension type and helps ensure that the sketch adheres to the defined measurements, which is critical for maintaining design intent and model accuracy.

In contrast, the other icons represent different tools or features within SolidWorks. For instance, the single line might relate to line drawing tools, the circle to creating circular features, and the triangle could indicate a different function altogether, which does not involve dimensional annotations. Understanding these distinctions is crucial for effective sketching and modeling in SolidWorks.