What is the significance of section lines in designs?

Section lines are essential in technical drawings as they indicate cutting planes where a section view is taken. This graphical representation helps convey how the interior structure of an object appears when it has been "cut" along a certain plane. These lines are typically shown as parallel diagonal lines and differentiate between different sections of an object, enabling a clearer understanding of its form and features that may not be visible in the exterior views.

In contrast, other options do not accurately describe the role of section lines. Fasteners would be noted in a different manner, such as through specific symbols or annotations. Overall dimensions are typically indicated with measurement lines, while quality controls are not represented through section lines but rather through specific notes or symbols pertaining to manufacturing standards. Thus, the indication of cutting planes versus other functions highlighted in the options reinforces the unique purpose of section lines in technical design.