Vocabulary Terms
You may have heard the saying, “A picture is worth a thousand words.” This is especially true for technical drawings.
Engineers, designers, and architects work with complex objects. It would be very difficult to describe the exact shape, size, and details of these objects using only words. For this reason, drawings have become the main language of industry. People in many trades—engineers, designers, technicians, and skilled workers—use drawings to communicate how products should be built, assembled, or repaired.
When you study Print Reading, you are learning how to understand this graphic language. One of the most important parts of this language is lines.
Technical drawings are made from many different types of lines. Each line has a special meaning. The first step in learning to read a drawing is learning what each type of line tells you. There are 11 basic line types, and each type has a specific form and weight (how thick or thin the line is). When these lines are used together in a drawing, they give you important information about the object.
Being able to read blueprints and build objects correctly is an important skill for all trades. Like any new skill, it takes time, practice, and patience to learn. But as you build your understanding, you will become more confident and successful in your work.
Video Explanation
Watch this 11:03 video, Blueprint Basic Lines, by weldZcool, Sep 22, 2020.
Object Line
A visible line, or object line is a thick continuous line, used to outline the visible edges or contours of an object.
Hidden Line
A hidden line, also known as a hidden object line is a medium weight line, made of short dashes about 1/8” long with 1/16”gaps, to show edges, surfaces and corners which cannot be seen. Sometimes they are used to make a drawing easier to understand. Often they are omitted in an isometric view.
Section Line
Section lines are used to show the cut surfaces of an object in section views. They are fine, dark lines. Various types of section lines may indicate the type of material cut by the cutting plane line.
Center Line
Center lines are used to indicate the centers of holes, arcs, and symmetrical objects. They are very thin (size), long-short-long kinds of lines.
Dimension Line
Dimension lines are thin and are used to show the actual size of an object. There are arrowheads at both end that terminate at the extension lines.
Extension Line
Extension lines are also thin lines, showing the limits of dimensions. Dimension line arrowheads touch extension lines.
Leader Line
Leaders are more thin lines used to point to an area of a drawing requiring a note for explanation. They are preferably drawn at a 45° angles.
Cutting Plane Line
A cutting plane line (very heavy) helps to show the internal shape at a part or assembly by slicing through the object.
Break Line
There are three kinds of break lines used in drawings. They are used to remove, or ‘break out” part of a drawing for clarity, and also to shorten objects which have the same shape throughout their length and may be too long to place on the drawing.
Short and long break lines are used for flat surfaces. Cylindrical are used on rods, dowels, etc.
Phantom Line
Phantom lines are long-short-short-long lines most often used to show the travel or movement of an object or a part in alternate positions. It can also be used to show adjacent objects or features.
Border Line
Borderlines are very thick, continuous lines used to show the boundary of the drawing or to separate different objects drawn on one sheet. They are also used to separate the title block form the rest of the drawing.
Questions
Directions: Name the types of lines shown below. Check your own answers
Identify the various line types used in this drawing. Click on the image to open a link to print.
Questions
Name the types of lines. Check your own answers.
Practice
Directions: Draw and identify the lines needed to complete the figures as indicated.
Click here for a copy of the worksheet to print.
Questions
Online Practice
Alphabet of Lines – YouTube an explanation by Hollis Watkins.
Basic Types of Lines Used in Engineering Drawings by WiscTechOpen.org/wisc-online (2026)
