Mastering Patent Drawing Line Types & Thickness in Compliance with MPEP, EPO, WIPO + Modern Software & Practical Tips

Introduction

Patent drawings are much more than visual aids—they are legal tools that communicate the boundaries and nature of your invention. Misuse of line types or incorrect line thickness can lead to objections, rejections, or even the misinterpretation of what’s being claimed.

This week’s SNS Patent Drafting feature explores every line type used in patent illustration, clarifies the MPEP, EPO, and WIPO standards, translates line weights into software-compatible units, and offers real-world best practices to avoid technical issues during submission and review.

Why Patent Drawing Line Types Matter

Each line in a drawing has a specific legal meaning:

• Solid lines = claimed portions

• Dashed lines = unclaimed subject matter

• Phantom lines = positioning/context

• Shading = surface depth and texture

• Hidden/center/section lines = internal or symmetrical details

• Lead lines = connect reference numerals to parts of the drawing

• Boundary breaks = indicate partial or fragmentary views

Failure to use these lines properly can create confusion and delay prosecution.

All Patent Drawing Line Types and Their Uses

Line Type	Description	Purpose
Solid lines	Bold, continuous lines	Define and claim the invention
Dashed lines	Thin, broken lines	Indicate unclaimed or optional features
Phantom lines	Suggest outline or position, often with alternating short/long dashes	Provide spatial context without claiming
Shading lines	Thin, close parallel lines	Depict contours, surface curvature, or texture
Hidden lines	Dashed lines inside the object	Show interior or obscured features (utility)
Center lines	Alternating long-short-long dash pattern	Represent axes of symmetry or rotation
Section lines	Diagonal hatch marks	Indicate surfaces in cross-section views
Boundary breaks	Jagged or wavy lines	Show intentionally incomplete parts of a drawing
Lead lines	Straight lines connecting parts to numbers	Point to elements referenced in the spec or figure legend

Recommended Thicknesses by Line Type

Line Type	Recommended Thickness (mm)	Software Stroke (pt)	Notes
Solid (Claimed)	0.3 – 0.7 mm	0.85 – 2 pt	Primary detail, must be legible when reduced
Dashed (Unclaimed)	0.2 – 0.3 mm	0.57 – 0.85 pt	Lighter than solid to avoid claim confusion
Phantom	0.2 – 0.25 mm	0.57 – 0.71 pt	Often short-long pattern, use consistently
Shading	0.1 – 0.2 mm	0.28 – 0.57 pt	Light from top left & keep irregular
Hidden	0.2 – 0.3 mm	0.57 – 0.85 pt	Applies to utility drawings
Center	0.2 mm	0.57 pt	Long-short-long pattern
Section	0.1 – 0.2 mm	0.28 – 0.57 pt	Use evenly spaced hatch lines
Boundary Break	0.25 mm	0.71 pt	Use consistently to show view breaks
Lead Lines	0.2 – 0.3 mm	0.57 – 0.85 pt	Should not touch the part, end with reference #

Modern File & Software Considerations

Why Line Appearance Varies

Despite your best efforts, your drawings may look different to an examiner or attorney because of:

• Printer DPI & Type: Laser printers vs inkjets may render fine lines unevenly.

• PDF Conversion Tools: Some converters flatten or rasterize line styles.

• Software Interpretation: Viewing drawings in Adobe Acrobat, MS Word, or Patent Center can introduce display inconsistencies.

• Submission Compression: USPTO & EPO file handlers may downsample PDFs or re-render vector data.

Best Practice: Use Layers

To combat these inconsistencies:

✅ Group similar line types in layers (e.g., solid lines, phantom lines, lead lines)

✅ Name layers clearly: Lead_Lines, Dashed_Unclaimed, Shading, etc.

✅ When asked to “bold” a set of lines or remove shading, you can make changes quickly

✅ Avoid having all lines in one layer—it makes editing tedious and prone to error

Quick Conversion Table: Points to Millimeters

Unit	Metric Equivalent
0.25 pt	≈ 0.088 mm
0.5 pt	≈ 0.176 mm
1 pt	≈ 0.353 mm
2 pt	≈ 0.706 mm
1 px @ 96dpi	≈ 0.26 mm

Conclusion

Patent drawings are both technical documents and legal representations. A precise understanding of line types, thicknesses, and visual clarity—alongside practical knowledge of how drawings are printed, viewed, and edited—is essential to producing patent illustrations that get approved without hassle.

At SNS Patent Drafting, we prepare every drawing with compliance, editability, and examiner clarity in mind—so you and your client never need to worry about technical objections or drawing rejections.

Need patent drawings revised or built to global specs from scratch?

Contact SNS Patent Drafting for compliant, layered, and examiner-ready illustrations.