diameter, around the dash number, and carry a leader
line to the part.
A dash and number are used to identify modified or
improved parts, and also to identify right-hand and
left-hand parts. Many aircraft parts on the left-hand side
of an aircraft are exactly like the corresponding parts on
the right-hand side but in reverse. The left-hand parts
are usually shown in the drawing.
Above the title block on some prints you may see a
notation such as "159674 LH shown; 159674-1 RH
opposite." Both parts carry the same number. But the
part called for is distinguished by a dash and number.
(LH means left-hand, and RH means right-hand.) Some
companies use odd numbers for right-hand parts and
even numbers for left-hand parts.
Drawing Lines
The lines used in working drawings are more than a
means of showing a picture of an object for the purpose
of building or repairing. The way a line is drawn has a
definite meaning.
Thick lines are used for the visible outline of the
object being drawn. Medium lines are used for the
dotted lines representing hidden features and for
cutting-plane,
short-break,
adjacent-part,
and
alternate-position lines. Center lines, dimension lines,
long-break lines, ditto lines, extension lines, and
section lines are represented by thin lines.
To understand blueprint reading, you must know
the different types of lines used in general drawing
practice and the information conveyed by each. Some
of the lines of major importance are illustrated in
1-5
Figure 1-4.—Blueprint title blocks. (A) Naval Ship's Systems Command; (B) Naval Facilities Engineering Command.
