Metric Units
   Metric Conversions
   Metrics in Drafting
     Paper Sizes
     Drawing Sheet Layout
   • Pen Sizes
        and Line Types

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Pen Sizes and Line Types

The ISO defines a set of standard metric line widths for drafting.

Like the ISO A and B series sheet sizes, the pen sizes increase by a factor of square root2. This allows additions and corrections to be made on the enlargements or reductions of drawings.

Each width is assigned a color code. The color code corresponds to that for the matching lettering stencil.

Line widths and color codes are standardized across all manufacturers.

Line Types

Letter Type of Line Line Thickness (mm) Application
    A0 A1 A2
A Continuous - thick
  • Visible outlines
B Continuous - thin


  • Fictitious outlines
  • Imaginary intersection of surfaces
  • Dimension lines, projection lines, intersection lines and leaders
  • Hatching
  • Outlines of revolved sections
  • Adjacent parts and tooling
  • Fold and tangent bend lines
  • Short centerlines
C Continuous - thin, freehand or ruled with zig-zag


  • Indication of repeated detail
  • Break lines (other than on an axis)
D Dashed - medium


  • Hidden outlines
E Chain - thin


  • Centerlines
  • Pitch lines
  • Alternative position of moving part
  • Path lines for indicating movement
  • Features in front of a cutting plane
  • Developed views
  • Material to be removed
F Chain - thick at ends and at change of direction, thin elsewhere


  • Cutting planes
G Chain - thick
  • Indication of surfaces to meet special requirements