What are the Different Types of Line Weight?
Line weight refers to the thickness (width) of lines used in technical drawings. Different line weights create visual contrast, helping engineers, architects, and manufacturers distinguish between various features.
According to engineering drawing standards such as ISO 128 and ASME Y14.2, line weights are generally categorized into thick and thin lines, with several standard thickness values.
Types of Line Weight
1. Very Thin Line
Typical Thickness: 0.13–0.18 mm
Uses
- Construction lines
- Fine details
- Small lettering
- Reference lines
2. Thin Line
Typical Thickness: 0.25–0.35 mm
Uses
- Dimension lines
- Extension lines
- Leader lines
- Hidden lines
- Center lines
- Section (hatching) lines
- Projection lines
This is the most commonly used line weight for supporting information.
3. Medium Line
Typical Thickness: 0.35–0.50 mm
Uses
- Secondary outlines
- Larger details
- General engineering drawings
- Some visible edges in smaller-scale drawings
4. Thick Line
Typical Thickness: 0.50–0.70 mm
Uses
- Visible object outlines
- Main edges
- Cutting plane lines
- Important boundaries
This is the most common line weight for visible features.
5. Extra Thick Line
Typical Thickness: 0.70–1.00 mm
Uses
- Drawing borders
- Emphasized features
- Large section cuts
- Special symbols
Standard Line Weight Series
Many CAD programs and drawing standards use the following standard line weights:
| Line Weight (mm) | Typical Application |
|---|---|
| 0.13 | Fine construction lines |
| 0.18 | Fine details |
| 0.25 | Dimensions and extension lines |
| 0.35 | Hidden and center lines |
| 0.50 | Visible object lines |
| 0.70 | Cutting planes and borders |
| 1.00 | Heavy emphasis and large borders |
Line Weight by Line Type
| Line Type | Typical Line Weight |
|---|---|
| Visible (Object) Line | Thick (0.50–0.70 mm) |
| Hidden Line | Thin (0.25–0.35 mm) |
| Center Line | Thin (0.25–0.35 mm) |
| Dimension Line | Thin (0.25 mm) |
| Extension Line | Thin (0.25 mm) |
| Leader Line | Thin (0.25 mm) |
| Section (Hatching) Line | Thin (0.25 mm) |
| Cutting Plane Line | Thick (0.70 mm) |
| Border Line | Extra Thick (0.70–1.00 mm) |
Thick vs Thin Lines
| Thick Lines | Thin Lines |
|---|---|
| Visible outlines | Dimension lines |
| Cutting planes | Extension lines |
| Borders | Hidden lines |
| Main edges | Center lines |
| Important features | Hatching and leader lines |
Line Weight Ratio
Engineering standards often recommend a 2:1 ratio between thick and thin lines.
Example:
- Thin line = 0.35 mm
- Thick line = 0.70 mm
This ratio creates clear visual distinction and improves readability.
Line Weight in CAD Software
Most CAD software, such as AutoCAD, SolidWorks, and DraftSight, allows you to assign line weights to layers.
Example layer setup:
| Layer | Line Weight |
|---|---|
| Object | 0.50 mm |
| Hidden | 0.35 mm |
| Center | 0.25 mm |
| Dimensions | 0.25 mm |
| Text | 0.18 mm |
| Border | 0.70 mm |
Importance of Using Correct Line Weights
- Improves drawing clarity
- Creates visual hierarchy
- Makes drawings easier to interpret
- Helps prevent manufacturing errors
- Complies with international drafting standards
- Produces professional-quality engineering drawings
Summary
The main types of line weight are:
- Very Thin (0.13–0.18 mm)
- Thin (0.25–0.35 mm)
- Medium (0.35–0.50 mm)
- Thick (0.50–0.70 mm)
- Extra Thick (0.70–1.00 mm)
In technical drawings, thick lines emphasize visible outlines and cutting planes, while thin lines are used for dimensions, hidden features, centerlines, and hatching. Proper use of line weights ensures drawings are clear, readable, and compliant with engineering standards.
Also Read: Architectural Line Weights.
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