Symbols have never been an insignificant part of human communication, especially in technical and scientific contexts. In engineering, symbols are a language of precision. Perhaps one of the most vital and internationally accepted symbols in engineering drawings is the Third Angle Projection Symbol. It is a tiny but vital mark representing a method of projecting three-dimensional objects onto two-dimensional surfaces, a fundamental core of modern design and production.
The third angle projection symbol is found on blueprints, CAD designs, and industrial documents across the globe. Architects, drafters, and engineers use it to prevent ambiguity and ensure clarity in visual description. This article discusses the meaning, origin, representation, and use of the third angle projection symbol and why it’s unavoidable in contemporary engineering communication.
Knowing What the Third Angle Projection Symbol Is
Third Angle Projection Symbol is a small illustration that denotes the projection technique used in a technical drawing. It shows how a three-dimensional object is being projected onto two-dimensional planes. It helps one reading the drawing to understand whether the projection views are ordered as per the first angle or third angle system.
The symbol looks like a truncated cone, as viewed from two sides:
- A side view, with a triangular cone pointing towards the right.
- A front view, with a circle representing the base of the cone.
The positioning of these figures establishes whether it’s a first angle or a third angle projection. Under third angle projection, the circle is on the right-hand side of the cone, so that the right-hand side view is projected on the right-hand side of the front view on the drawing.
History and Origin of the Third Angle Projection Symbol
The use of projection systems began with the development of descriptive geometry in the 18th century. The engineers and mathematicians needed a system to project 3D objects correctly onto paper. Gaspard Monge, a French mathematician, is well known for creating the concept of orthographic projection during the late 1700s.
In Europe, First Angle Projection was the convention placing views opposite their actual position. However, in North America, engineers found it more convenient to deal with the Third Angle Projection where views are placed on the same side of the object as its view.
To avoid confusion between these two systems, a standard symbol was created. The Third Angle Projection Symbol was by the early 20th century officially accepted by ANSI (American National Standards Institute) and ASME (American Society of Mechanical Engineers), while the First Angle Projection Symbol was adopted by ISO to be employed in countries in Europe.
Symbolization of the Third Angle Projection Symbol
The symbol is not a picture; it is a visual code. The third angle projection symbol is as below:
| Part of Symbol | Representation | Meaning |
| Left part | Truncated cone (side view) | Represents the way the object looks from the side |
| Right part | Circle (front view) | Represents the front face or base of the cone |
| Arrangement | Circle to the right of the cone | Signals third angle projection |
| Orientation | Arrow points to the right | Direction of projection |
The third angle projection involves the object standing between the viewing direction and the plane of projection. Here, the right part of the object is on the right, the left on the left, and the top above the front. It is the manner in which man intuitively conceives objects and thus is utilized in the USA, Canada, and other Asian countries.
Difference Between Third and First Angle Projection
The Third Angle and First Angle systems often puzzle students and junior engineers. It is essential to comprehend their difference to read technical drawings with accuracy.
| Aspect | First Angle Projection | Third Angle Projection |
| Placement of object | Between observer and projection plane | Between projection plane and observer |
| Position of right-side view | Drawn on right side of front view | Drawn on left side of front view |
| Position of top view | Drawn below the front view | Drawn above the front view |
| Common usage | Europe, Asia (ISO standard) | USA, Canada, UK, Australia (ANSI standard) |
| Symbol arrangement | Circle on left of cone | Circle on right of cone |
The third angle projection can be considered to be more intuitive as it seems closer to the way we perceive in real life what you see, is where it’s at on the drawing.
Purpose and Importance of the Third Angle Projection Symbol
The raison d’être for the Third Angle Projection Symbol is to avoid confusion between engineering drawings. A drawing prepared in the first angle system may look almost the same as a drawing prepared in the third angle system, but the locations of views will be different. Having the projection symbol ensures that any engineer, producer, or machine operator who views the drawing will know which standard is in use.
Its relevance entails:
- Clarity and Communication: Enables international teams to understand drawings without the issue of language.
- Consistency in Manufacturing: Prevents manufacturing errors by uniquely differentiating view orientations.
- Conformity to Standards: Most industries require drawings to include the projection symbol so that they meet ISO or ANSI standards.
- Educational Use: Engineering graphics learning of projection systems relies on recognizing and understanding the symbol.
Third Angle Projection Symbol in Engineering Drawings
In a traditional technical drawing, the symbol would usually be in the title block or to the side of the drawing scale. It ensures that the method of projection is realized before the drawing is read.
Examples:
- The top view (plan) is above the front view.
- The right side view is to the right of the front view.
- The left side view is to the left of the front view.
This standard layout follows the principle that the viewer looks at every face of the object.
Steps to Insert Third Angle Projection Symbol in Word or CAD Software
Students, engineers, or drafters can be asked to insert this symbol in their reports or design documents. Depending on the software, different steps can be followed to insert it.
| Method | Steps |
| In Microsoft Word or PowerPoint | Insert → Picture → Upload image of third angle projection symbol |
| In AutoCAD or SolidWorks | Use the standard projection symbol from the default library |
| In CATIA, Fusion 360, or Inventor | Part of drawing templates by default |
| Manual Drawing | Draw a truncated cone and circle and label appropriately |
| Unicode/Copy | Not an ANSI character; use as image or custom block |
In commercial CAD platforms, the symbol will be automatically placed when converting the drawing standard to ANSI.
Third Angle Projection in Real Life and Industry
The third angle projection system is used in nearly all mechanical, civil, and architectural fields of nations adopting American or British standards. It is the foundation for:
- Mechanical parts such as gears, engines, and machine tools
- Architectural sketches showing elevation and section
- Electrical and civil engineering drawings
Motor vehicle, aircraft, and building construction industries are highly dependent on third angle projection to communicate design intention effectively to fabricators and technicians.
Also Read: FF Symbol: Meaning, Origin, Use, and Digital Function
Why Third Angle Projection System Becomes Popular
The third angle projection system has different benefits which have contributed to it being generally popular all over the world:
- Natural Visualization: Views are organized in such a way that people see naturally.
- Ease of Learning: Students learn it more easily.
- Error Minimization: Reduces possibilities for reflection or inverted view interpretation.
- Compliance with CAD: Computer-based software is designed for third angle projection.
Due to these facts, it is often the default taught at engineering schools in non-continent Europe.
The Psychology of Symbols of Technical Drawing
Symbols like the third angle projection do more than convey rules they train the brain to think spatially. Psychologists studying visual cognition among engineers found that consistent symbols allow experts to visualize 3D shapes earlier and more accurately.
The pairing of triangle and circle in the projection symbol creates a pattern response at once, so even novice designers automatically understand projection layout on a subconscious level. That visual trigger speeds up understanding and minimizes errors in interpretation of design.
The Role of Standards Organizations
Two main standards govern use of the third angle projection symbol:
- ANSI/ASME Y14.3 (American Standard)
- ISO 5456 (International Standard)
ANSI prefers third angle projection but ISO accommodates both systems with a preference to clearly indicate the symbol. Adherence to these facilitates international uniformity, especially in international collaboration where drawings are exchanged among manufacturers.
The Third Angle Projection Symbol is small in a technical drawing but its impact is enormous. It makes worldwide communication within the engineering sector possible, so manufacturing and design teams will never get confused with each other. From its origins in historic geometric practices to its presence in today’s CAD settings, the symbol is about simplicity, precision, and worldwide comprehension.
Whenever an engineer sees that little cone-and-circle sign, they instantly can interpret the drawing. It is more than a mark; it’s a tie between nations, machines, and brains, an engineering language of exactness that doesn’t use words.
Frequently Asked Questions
What does the symbol for the third angle projection mean?
It shows that the third angle projection system is employed by the views of drawings, where the object is between the observer and the projection plane.
Who created the third angle projection system?
It was evolved from descriptive geometry’s concepts by Gaspard Monge and later standardized by ANSI.
Where is the third angle projection used?
It is extensively used in the United States, Canada, the UK, and the majority of Asian nations.
What is the difference between third and first angle projection?
In first angle projection, the object is between the plane and observer; third angle projection has the observer between the plane and the object.
Where is the projection symbol in a drawing located?
It is generally in the title block of an engineering drawing to indicate the projection method employed.