Types of Lines in Engineering Drawing: Uses & Precedence

In this article, we discuss various types of lines used in Engineering Drawing.

What is a Line?

In geometry and engineering drawing, a line is a fundamental element used to represent shapes, dimensions, and boundaries. It is a one-dimensional object that extends infinitely in both directions (in mathematical terms) or is defined with a specific length in practical applications.

Types of Lines used in Engineering Drawing

The types of lines used in Engineering Drawing is described below:

Here’s a table summarizing the different types of lines used in engineering drawing:

Line Type	Purpose	Appearance
Object (Visible) Line	Represents visible edges of an object	Thick, continuous (―)
Hidden Line	Shows edges or features not visible in the view	Dashed (_ _ _ _)
Center Line	Indicates the center of circles or symmetry	Long-short dashes (— · — · —)
Dimension Line	Indicates size (length, width, height)	Thin with arrows (← 50 mm →)
Extension Line	Extends from the object to mark dimensions	Thin solid line
Leader Line	Connects notes or dimensions to a feature	Thin line with an arrow
Section (Cutting Plane) Line	Shows surfaces that have been cut through	Thick dashed or solid line with arrows
Hatching (Section) Lines	Used to represent material surfaces in section views	Thin diagonal lines (/////)
Break Line	Shortens long objects in drawings	Zigzag or wavy line
Phantom Line	Represents alternate positions of parts	Long-short-short dashes (— ·· — ·· —)
Border Line	Defines the boundary of the drawing sheet	Thick continuous line

Why Should We Use Different Lines in Engineering Drawing?

Using different types of lines in engineering drawing is essential for clear communication, accuracy, and standardization. Here’s why:

Clarity & Readability
Standardization & Consistency
Accuracy & Precision
Differentiation of Features
Effective Communication
Saves Time & Cost

Precedence of Lines:

When different types of lines overlap or intersect in a technical drawing, a specific hierarchy is followed to prioritize visibility and importance. This is called the Precedence of Lines. The general rule is:

1. Visible (Object) Lines – Highest Priority

Always take precedence over other lines.
Represent the actual shape and edges of the object.

2. Hidden Lines

Take priority over center lines but are secondary to visible lines.
Show features that are not directly visible.

3. Cutting Plane Lines

Used for sectional views, typically override center and phantom lines.

4. Center Lines

Indicate axes of symmetry, holes, or cylindrical features.
Take precedence over dimension and extension lines but are secondary to object and hidden lines.

5. Dimension & Extension Lines

Provide measurements but never interfere with object, hidden, or center lines.
They should not cross or overlap critical lines unless necessary.

6. Section (Hatching) Lines

Used to indicate material cut in sectional views.
Should not dominate the drawing and must remain thin.

7. Phantom Lines – Lowest Priority

Represent alternate positions of parts or movement paths.
Do not interfere with more critical lines like object or hidden lines.

Key Rule: More critical features should always be visible, while less important ones should remain in the background.

Conclusion

Lines in engineering drawing are essential for clear, precise, and standardized communication. Each type of line serves a specific purpose, ensuring that drawings are easy to interpret by engineers, manufacturers, and construction professionals. The precedence of lines helps maintain clarity when multiple lines overlap, ensuring that the most important details remain visible.

By following proper line conventions, engineering drawings become a universal language that eliminates confusion, reduces errors, and improves efficiency in design, manufacturing, and construction processes. Mastering these line types is crucial for anyone working in technical fields.