Final answer:
The thickest lines on an engineering drawing are the object lines, which indicate the visible edges of an object. Other types of lines like hidden lines, center lines, and extension lines have different purposes and are represented with thinner lines.
Step-by-step explanation:
On an engineering drawing, the lines that appear the thickest are the object lines. These lines are used to represent the edges and contours of an object that are visible to the viewer. The thickness of the object lines helps them stand out against other types of lines, such as hidden lines, center lines, and extension lines. Hidden lines are used to represent the edges that are not directly visible, and they are typically drawn as dashed lines. Center lines represent axes of symmetry and are also used for circles and holes; these are usually represented by alternating long and short dashes. Extension lines are used to show the limits of dimensions and do not touch the object but are drawn parallel to it. While the object lines are the thickest to enhance the visibility of the object's edges, other lines like hidden lines and center lines are drawn thinner to denote their different purposes.
p>Hatching is another technique used in engineering drawings; it consists of closely spaced lines to show shading and shadows, which helps in giving objects a sense of form and three-dimensionality. In an engineering context, hatching might not imply line thickness but rather the density and angle of the lines to depict surface texture or shadow in cross-sectional views.