What do section lines indicate in an engineering drawing?

Section lines in an engineering drawing are used specifically to indicate the imaginary cut portion of the part in a section view. When a drawing includes a section view, it helps visualize the internal features of a part as if it has been cut through. The section lines, often represented as closely spaced parallel lines, fill the area of the cut surface to distinguish it from other parts of the drawing and to convey important information about the internal structure.

These lines enhance clarity in understanding the configuration and arrangement of internal elements, which would be otherwise hidden in a standard view. Proper use of section lines allows engineers and manufacturers to communicate design intent effectively and ensures that all parties involved have a clear understanding of the component's internal geometries and features.