Dimension and Extension Lines Technology

 

Dimension and Extension Lines Technology

In technical drawing (engineering graphics, drafting, CAD, etc.), dimension lines and extension lines are essential for accurately conveying the size, shape, and location of objects. They are part of the drawing standards defined by organizations like ISO, BIS, and ANSI.

1. Dimension Lines

• Definition: Thin, continuous lines terminated with arrowheads that indicate the distance between two points on an object.

• Purpose: Show measurements (length, width, diameter, angle, etc.) of a feature.

• Features:

  • Drawn parallel to the feature being measured.

  • Numerical value (dimension figure) is placed above, at the center of the line.

  • Terminated with arrowheads, dots, or oblique strokes depending on standard.

• Types:

  • Linear dimension line – for straight distances.

  • Angular dimension line – for angles, shown as an arc.

  • Radial/diameter dimension line – for circles and arcs.

2. Extension Lines

• Definition: Thin lines that extend from the object’s edges or features to the dimension line.

• Purpose: Indicate the exact points on the object to which the dimension applies.

• Features:

  • Drawn perpendicular to the dimension line.

  • Start a small gap away from the object line (so they don’t touch).

  • Extend slightly beyond the dimension line for clarity.

  • Should not cross dimension lines unnecessarily.

3. Technology / Importance

• Provide a universal language in engineering, ensuring accurate communication of size and geometry.

• Used in manual drafting (drawing boards, T-squares, set-squares, pencils) and in modern CAD software (AutoCAD, SolidWorks, CATIA, etc.), where dimensioning tools automatically generate these lines.

• Follow standards (e.g., ISO 129-1, ANSI Y14.5) so that drawings are readable worldwide.

Summary:

• Dimension lines carry the measurement value.

• Extension lines link the measurement to the object.
  Together, they form the dimensioning system, which is the backbone of precise technical communication in engineering and manufacturing.