Topic 05- Line Types and Dimensions in Engineering drawing

Introduction to lines

The article talks about Line Types and Dimensions in Engineering drawing. The most fundamental parameter to define any engineering design is a point. The set of these points is called a line. Just as the points can be arranged in a number of fashions. This gives rise to number of important line types. These will be discussed shortly.

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Introduction to dimensions

The next important thing is the method of dimensioning. An object is made up of lines. We can easily draw lines of an object, but we need dimensions to compare them quantitatively. Hence there are some types of dimensioning and there are some rules that we have to keep in mind while writing about dimensions.

Important Line Types

Some of the important Line types are elaborated below

How to Read Engineering Drawings – a Simple Guide | Make UK
Line Types

Object Line

Solid thick line. Used to indicate visible object of an object.

Hidden Line

Dashed thin line. Used to indicate hidden edges, corners hidden in a particular view

Extension Line

Thin line. Used to extend the edge, face or corner of a geometric feature.

Dimension Line

Thin line with arrows. Used to indicate the size or location of the geometric feature.

Leader Line

Thin line with arrow or dot. Used to indicate the size a geometric feature. Arrowheads touch object lines. Dots are placed on faces or surfaces.


Alternating long-short-long dashed thin line. Used to denote the axis of rotational parts or center point of holes.

Symmetry Lines

Centerline with 2 thick perpendicular track marks at each end. Used when partial symmetrical views are drawn.


Some lines have higher precedence than other according to their importance in the final drawing.


Quantitatively, Dimension means to associate a number expressed in appropriate units of measurement and indicated graphically on technical drawings with different features.

Types of dimensioning

There are two main types of dimensioning. These are aligned and unidirectional.

Aligned system

Dimensions are written perpendicular to the dimension line so that they may be read from the bottom or right-hand side of the paper. It is placed at the middle and on top of the dimension lines.

Unidirectional system

dimensions are placed in such a way that they can be read from the bottom edge of the drawing sheet only.

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