How is an extension line different from a dimension line?

An extension line serves a specific purpose in technical drawings, particularly in dimensioning. It is drawn from a feature on the object to indicate where a dimension begins or ends, thus providing clarity and precision in interpreting the measurement. These lines are crucial for understanding the exact points that are being referenced in a dimension, allowing fabricators and welders to accurately identify where cuts, welds, and other operations need to take place.

This differentiates the extension line significantly from dimension lines, which actually contain the numerical value of the dimension and typically have arrowheads at both ends to indicate what is being measured. By establishing a clear connection between a feature and its corresponding measurement, extension lines ensure that the intent of the drawing is communicated effectively.

Therefore, option C highlights the primary function and importance of extension lines in the dimensioning process, setting them apart from other types of lines used in technical drawings.