Pen Sizes and Line Types (Metric)

By Steve
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 2. 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.
LetterType of LineLine Thickness (mm)Application
AContinuous - thick
  • Visible outlines
BContinuous - 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
CContinuous - thin, freehand or ruled with zig-zag

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

  • Hidden outlines
EChain - 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
FChain - thick at ends and at change of direction, thin elsewhere

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