What do the hidden lines of a product drawing show?

The hidden lines of a product drawing are specifically used to indicate features that are not visible from the external viewpoint of the object. These lines typically represent edges or contours of features located behind or beneath the visible surfaces, such as internal holes, cutouts, or other geometrical details that are part of the design but can't be seen directly from the outside. The use of hidden lines helps convey comprehensive information about the part's geometry, making it clearer for the viewer to understand the complete structure and functionality of the object being designed.

In a product drawing context, the ability to depict hidden features is crucial for manufacturing and assembly processes where understanding these internal characteristics is necessary for accurate fabrication and quality control. Thus, the correct answer emphasizes the role of hidden lines in providing insight into the internal aspects of a part that are crucial for a complete understanding of its design.