Extension Lines

Extension lines are used in dimensioning to show the size of an object. Extension lines are thin, dark, solid lines that extend from an object at the exact locations between which dimensions are to be placed. A space of approximately 1/16 inch is usually allowed between the object and the beginning of the extension line (Figure 3.6). Plan to avoid crossing other extension lines and/or dimension lines.

Extension lines are fine lines that relate the dimension lines to their features. They do not touch the features; instead they start about 1/6 inch (4.23 mm) from the feature and extend about 1/8 inch (3.175 mm) beyond the arrowheads of the dimension line.

Extension lines show the extent of a dimension, and dimension lines show the length of the dimension and terminate at the related extension lines with slashes, arrowheads, or dots. The dimension number in feet and inches is placed above and near the center of the solid dimension line.

Figure 3.5A Center lines indicate the centers of circles, arcs, and symmetrical objects.

ELEVATION

Figure 3.5A Center lines indicate the centers of circles, arcs, and symmetrical objects.

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