Alphabet of Lines
Alphabet of Lines
 Industry standard classifying the
different types of lines used in
drawings.
 Developed by the American Society of
Mechanical Engineers (ASME).
 Lines are classified by line thickness
and drawn thin or thick.
Alphabet of Lines
Alphabet of Lines
 The American National Standards Institute (ANSI)
drafting standard applies.
• An approximate 2:1 line width ratio is used for manually
drawn thick and thin lines.
• For CAD drawings, a single line width is acceptable.
 Thick lines are typically drawn with a 0.7 mm or 0.9
mm mechanical pencil.
 Thin lines are typically drawn with a 0.3 mm or 0.5
mm mechanical pencil.
Alphabet of Lines
Construction Lines
 Used to initially lay out a drawing.
 Drawn very light and thin so they are
barely visible.
 Drawn with a 0.3 mm pencil or a
sharpened drafting pencil with a hard
lead.
Visible Lines
 Used to represent the visible edges of
an object.
 Also called object lines.
 Drawn thick and dark.
 Drawn with a 0.7 mm or 0.9 mm
drafting pencil with a soft lead.
Hidden Lines
 Used to represent edges hidden from
view.
 Drawn as thin, dark lines.
 Drawn as 3 mm dashes about 1.5 mm
apart.
 Spacing can vary slightly.
Centerlines
 Used to show the center of circles and arcs.
 Drawn as thin lines.
 Drawn using two long dashes and a short
dash separated by a 1.5 mm gap.
 The short dash is drawn about 3 mm long at
the center point.
 The long dash extends beyond the circle.
Dimension Lines
 Used for dimensioning and notes.
 Drawn as thin lines.
 Drawn with arrowheads on each end
and placed between extension lines.
 A line break provides space for the
dimension.
Extension Lines
 Used to extend dimensions from the
related objects.
 Drawn as thin lines.
 Drawn with a short space between the
object and line.
 Extend about 3 mm beyond the
dimension line.
Leaders
 Used to point to notes or dimensions.
 Drawn as thin lines.
 Consist of an arrowhead and angled
line connected to a shoulder.
Break Lines
 Used to indicate part of the object has
been removed.
 Short break lines are drawn thick.
 Long break lines are drawn thin with
freehand “zigzags.”
Orthographic Projection
 A standard form of drawing using the
alphabet of lines.
 Several two-dimensional (2D) views of
the three-dimensional (3D) object
provide a complete description.
 Orthographic drawings are also known
as multiview drawings.