Which line defines the centers of arcs, circles, or symmetrical parts?

• A. Center Line
• B. Extension Line
• C. Dimension Line
• D. Object Line

Answer: (A)

Center lines are used to locate the centers of circles and arcs and to indicate axes of symmetry in a part. They run through the true center of round features and along the symmetry lines, helping you precisely position dimensions and relate features to each other. You can recognize them by their distinctive dash pattern, which sets them apart from other lines: extension lines extend features to dimensions, dimension lines carry the measurement, and object lines depict visible edges. So, the line that defines the centers of arcs, circles, or symmetrical parts is the center line.