What is the difference between first and third angle projection?

The views are the same, but they sit in different places. In third angle the top view goes above the front view and the right side view to the right. In first angle the top view goes below the front view and the right side view to the left.

Which countries use third angle projection?

The United States and Canada use third angle (ASME Y14.3). Most of Europe uses first angle. ISO 128 allows both, so always check the symbol in the title block.

How do I tell first and third angle from the symbol?

The symbol shows a truncated cone from the side and from the end. In third angle the small end of the cone points toward the circles. In first angle it points away from them.

What happens if I read the projection wrong?

You see the part mirrored. A hole on the left ends up on the right, and the part gets made wrong.

Drawing basics: lesson 2 of 5

First and third angle projection

Decide which view goes in the empty box. Get 10 right to finish. ASME practice uses third angle, ISO practice uses first angle.

Read the projection symbol. Which view goes in the box marked ?

Where the views go

A part is drawn from several sides. The front view sits in the middle and the other views are placed around it. The views look the same in both systems. Only their place on the sheet changes.

View	Third angle (US, ASME)	First angle (Europe, ISO)
Top view	Above the front view	Below the front view
Bottom view	Below the front view	Above the front view
Right side view	To the right of the front view	To the left of the front view
Left side view	To the left of the front view	To the right of the front view

A simple way to remember it: in third angle a view sits on the side it is seen from. In first angle it sits on the opposite side.

The projection symbol

The title block shows which system the drawing uses with a small symbol: a truncated cone drawn from the side and from the end. Look at the side view of the cone. In third angle its small end points toward the circles. In first angle its small end points away from them. The symbol can be drawn either way round, so go by the cone, not by which side the circles are on.

Third angle: small end toward the circles

First angle: small end away from the circles

Common mistakes

Assuming a drawing is third angle because the top view is on top. Check the symbol first.
Reading the symbol by where the circles are. They can be on either side.
Swapping left and right side views in first angle. The right side view is on the left.

Questions

What is the difference between first and third angle projection?: The views are the same, but they sit in different places. In third angle the top view goes above the front view and the right side view to the right. In first angle the top view goes below the front view and the right side view to the left.
Which countries use third angle projection?: The United States and Canada use third angle (ASME Y14.3). Most of Europe uses first angle. ISO 128 allows both, so always check the symbol in the title block.
How do I tell first and third angle from the symbol?: The symbol shows a truncated cone from the side and from the end. In third angle the small end of the cone points toward the circles. In first angle it points away from them.
What happens if I read the projection wrong?: You see the part mirrored. A hole on the left ends up on the right, and the part gets made wrong.

Explained in our own words and checked against several textbooks. For the full rules, see ASME Y14.2, ASME Y14.3, ISO 128, ISO 5456-2, ISO 7200 and ISO 2768-1.