For general engineering drawings, you must use the line types that the Bureau of Indian Standards recommends in Table 2. You also need to pick the line thickness based on the drawing’s type and size, choosing from any of the six groups listed in Table 1.
If you use other line thicknesses for special cases, like electrical or piping drawings, or if you use the lines from Table 2 for purposes not covered in the last column, you must explain your choices with notes right on the drawing.
Table 1: Thickness of lines (All dimensions in mm)
Types of Lines Used in Engineering Drawing
The following are the different types of lines used in engineering drawing:
- A type – Continuous Thick
- B type – Continuous THIN
- C type – Continuous THIN Freehand
- D type – Continuous THIN Zig-Zag
- E type – Dashes THICK
- F type – Dashes THIN
- G type – Chain THIN
- H type – Chain THIN and THICK
- J type – Chain THICK
- K type – Chain THIN Double Dash
Table 2: Thickness of Lines
Type A
Outline of Parts
Outline of Parts type lines show the visible edges of the objects, so they should stand out. Draw them as bold, thick, continuous lines.
Type B
Dimension, Projection, Leader, Hatching Lines
Draw Dimension, Projection, Leader, and Hatching type lines thin and continuous.
Run the extension lines for dimensioning straight from the outlines without leaving a gap, and let them extend a bit beyond the dimension lines. Use this type also to draw outlines of adjacent and revolved sections.
Type C
Limits or Boundaries of Partial or Interrupted Views
Draw Limits or Boundaries of Partial or Interrupted Views type lines as continuous, thin, wavy, freehand lines to show the limits or boundaries of partial or interrupted views.
Type D
Break Lines
Draw Break Lines type lines as ruled, short, zig-zag thin lines to show the breaks.
Type E
Hidden Lined (Thick)
Hidden Lined (Thick) type lines use thick short dashes, placed closely and evenly. Draw these lines to show hidden or invisible edges of the objects.
Type F
Hidden Lines (Thin)
Hidden Lines (Thin) type lines use thin short dashes, placed closely and evenly. Draw these lines to show hidden or invisible edges of the objects.
Although THICK lines of Type-E are recommended for showing the hidden edges, people usually prefer THIN lines of Type-F.
Type G
Centre lines, Lines of Symmetry, Trajectories, and Pitch Circles
Centre lines, Lines of Symmetry, Trajectories, and Pitch Circles type of lines are long, thin, chain lines with alternately long and short dashes. Keep the proportion between long and short dashes between 6:1 and 4:1, and space them evenly.
Once you pick a proportion, keep it the same through the whole drawing. Extend the center lines a short distance beyond the outline. Also draw these lines to represent lines of symmetry, trajectories, and pitch circles, etc.
Type H
Cutting Plane Lines
Cutting Plane Lines are long lines, thickened at the ends and thin elsewhere, with alternately long and short dashes. Keep the proportion between long and short dashes between 4:1 and 6:1, and space them evenly. Make the corners where the section plane changes direction thick for a short length.
Type J
Lines to indicate Surfaces which require Additional Treatment
These are long thick lines with alternately long and short dashes. Keep the proportion between long and short dashes between 6:1 and 4:1, and space them evenly. Draw these lines to indicate surfaces that need extra treatment like anodizing, plating, etc.
Type K
Lines to indicate Outlines of Adjacent parts, Extreme positions of Movable Parts, Centroidal lines, Parts situated in front of the Cutting Planes, Initial outlines before forming.
These are thin lines with a long dash and two short dashes alternately, spaced evenly in a proportion between 6:1 and 4:1.
Use these lines to show the outlines of adjacent parts, extreme positions of movable parts in assembly drawings, parts situated in front of the cutting planes, initial outlines before forming, and centroidal lines, etc.