Extensions are used to extend the line showing the side or edge of a figure for the purpose of placing a dimension to that side or edge. They are very narrow and have a short break where they extend from the object and extend a short distance past the arrow of the dimensioning line.
Sectioning lines indicate the exposed surfaces of an object in sectional view. They are generally thin full lines but may vary with the kind of material shown in section.
Phantom lines, composed of one long and two short evenly spaced dashes, indicate the alternate position of parts of the object or the relative position of a missing part.
Break lines indicate that a portion of the object is not shown on the drawing. Short breaks are made by solid, freehand lines. For long breaks, solid ruled lines with zigzags are used. Shafts, rods, tubes, and other such parts which have a portion of their length broken out have the ends of the break drawn as indicated in Figure 2-24.
Leader lines are solid lines with one arrowhead and indicate a part or portion to which a note, number, or other reference applies.
Hidden lines indicate invisible edges or contours. Hidden lines consist of short dashes evenly spaced and are frequently referred to as dash lines.
Outline or Visible Lines
The outline or visible line is used for all lines on the drawing representing visible lines on the object.
Stitch lines indicate stitching or sewing lines and consist of a series of evenly spaced dashes.
Cutting Plane and Viewing Plane Lines
Cutting plane lines indicate the plane in which a sectional view of the object is taken. In Figure 2-24, plane line A-A indicates the plane in which section A-A is taken.
Viewing plane lines indicate the plane from which a surface is viewed.
The drawings for a component are composed largely of symbols and conventions representing its shape and material. Symbols are the shorthand of drawing. They graphically portray the characteristics of a component with a minimal amount of drawing.
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