The document introduces the alphabet of lines used in technical drawings to convey different types of information. It describes five main line types - visible lines that show the outline and shape of objects, hidden lines that show hidden outlines, center lines that indicate the center of holes or symmetrical objects, dimension lines that show the size of features, and extension lines that show the location of dimensions. Being able to understand and properly employ these line types is essential for interpreting technical drawings.

1. Alphabet Of Lines
The backbone of drafting

2. Introduction to the Alphabet
of Lines
In order to understand what the drafter
is trying to get across, you must be able
to understand the symbols and lines he
uses.
Each line has a definite form and line
weight.

3. 5 Main Line Types
Visible
Hidden
Center
Dimension
Extension

4. Visible Lines
Dark, heavy lines.
Show the outline and shape of an
object. (SHOWS SHAPE)
Define features you can see in a
particular view.

5. Hidden Lines
Light, narrow, short, dashed lines.
Shows the outline of a feature that can
not be seen in a particular view.
Used to help clarify a feature, but can
be omitted if they clutter a drawing.

6. Center Lines
Thin line consisting of long and short
dashes.
Shows the center of holes, slots, paths
of rotation, and symmetrical objects.

7. Dimension Lines
Dark, heavy lines.
Show the length, width, and height of
the features of an object. (SHOWS
SIZE)
Terminated with arrowheads at the
end.

8. Extension Lines
Used to show the starting and stopping
points of a dimension. (SHOWS
LOCATION)
Must have at least a 1/16th space
between the object and the extension
line.
Extension Line
Dimension Line

9. Summary
Now that we have discussed the 5 main
line types, you should be able to do the
following:
1. Identify the alphabet of lines.
2. Identify where the line types are
used.
3. Produce the lines with correct
spacing and line weight.