What type of line illustrates the visible edges of an object in a technical drawing?

In technical drawings, visible lines are used to represent the outlines or edges of an object that are directly observable. These lines are typically drawn as solid lines, and they form the primary shape of the object depicted in the drawing. The main function of visible lines is to clearly convey the physical form and boundaries, allowing anyone reading the drawing to understand the geometry of the part being represented.

The other types of lines serve specific purposes. Hidden lines indicate edges that are not visible from the current viewpoint, center lines represent symmetry and are often used in conjunction with circles or arcs, and extension lines indicate the extent of dimensions. These lines do not illustrate the direct visible edges of an object, which is why they do not answer the question. Understanding the role of visible lines is crucial in reading and interpreting technical drawings accurately, as they provide the clear and straightforward representation necessary for effective communication in the field of welding and engineering.