convenient to draw a dimension line directly between
1-2.
LINE CONVENTIONS
the visible lines. There is always a small space
In order to include all the necessary information
between the extension line and the visible line.
on a drawing in a meaningful manner, different types
and weights of lines are used to represent the features
f. Leaders. A leader is a thin (light) line
of the object. The meaning of a line with certain
terminated with an arrowhead that is used to indicate
characteristics has been standardized, and will be the
the part or feature to which a number, note, or other
same on any drawing. These line conventions must
information refers.
be understood in order to read drawings. The line
conventions most often encountered in construction
g. Phantom Lines. A medium weight line
prints are described below and shown in figure 1-2.
made of long dashes broken by two short dashes is
Application of these line conventions are
called a phantom line and indicates one of three
demonstrated in figure 1-3.
things: the relative position of an absent part, an
alternative position of a part, or repeated detail which
a. Visible Lines. A heavyweight unbroken
is not drawn.
line is used for the primary feature of a drawing. For
drawings of objects, this line convention represents
h. Stitch Lines. A medium line made of short
the edges, the intersection of two surfaces, or the
dashes evenly spaced and labeled used to indicate
surface limit that is visible from the viewing angle of
stitching or sewing.
the drawing. This line is often called the outline.
i. Break Lines. A thin (light) line interrupted
b. Hidden Lines. A medium weight line of
by a z-shaped symbol. The break line indicates that
evenly spaced short dashes represents an edge, the
the object has been shortened to save space on the
intersection of two surfaces, or the surface limit
drawing. The true length is indicated by the
which is not visible from the viewing angle of the
dimension specified. The short break line convention
drawing.
varies with shape and material, figure 1-4, and
indicates that part of the object has been cut away to
c. Center Lines. A thin (light) line composed
show section detail or hidden features.
of alternate long and short dashes of consistent length
is called a center line. It is used to signify the center
j. Cutting Plane Lines. A pair of short, heavy
of a circle or arc and to divide an object into equal or
lines with arrowheads projected at 90 degrees
symmetrical parts.
indicates the cutting plane when a drawing includes a
section view. Letters (AA, BB, etc.) are usually
d. Dimension Lines. A solid continuous line
placed at the arrowheads to identify the section view.
terminating in arrowheads at each end. Dimension
The arrowheads show the viewing direction of the
lines are broken only to permit writing in dimension.
section view. Where necessary, the section lines may
On construction drawings the dimension lines are
be connected by a line of short, heavy dashes
unbroken. The points of the arrowheads touch the
indicating the exact path of the cutting plane.
extension lines which mark the limits of the
dimension. The dimension is expressed in feet and
k. Section Lines. When a drawing includes a
inches on architectural drawings and in feet and
section, the surface or surfaces which are in the
decimal fraction of a foot on engineering drawings.
cutting plane are indicated by section lines. When
the object sectioned is all one material, the section
e. Extension Lines. Extension line is a thin
lines are usually closely spaced parallel lines of
(light) unbroken line that is used to indicate the
medium thickness. Where different materials are
extent of the dimension lines. The extension line
involved, different section conventions are used to
extends the visible lines of an object when it is not
distinguish between them.
3
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