Metrics in Drafting - 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 root 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.

Line Types

Letter	Type of Line	Line Thickness (mm)			Application
		A0	A1	A2 A3 A4
A	Continuous - thick	0.7	0.5	0.35	Visible outlines
B	Continuous - thin	0.35	0.25	0.18	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	0.35	0.25	0.18	Indication of repeated detail Break lines (other than on an axis)
D	Dashed - medium	0.50	0.35	0.25	Hidden outlines
E	Chain - thin	0.35	0.25	0.18	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	0.7 0.35	0.5 0.25	0.35 0.18	Cutting planes
G	Chain - thick	0.7	0.5	0.35	Indication of surfaces to meet special requirements