First angle vs third angle projection: how orthographic views are arranged

A drawing shows a three-dimensional part as a set of flat views. Which view goes where depends on the projection method, and there are two in common use: first angle and third angle. They use exactly the same views; only the positions differ. Read a drawing with the wrong method in mind and every side view is on the wrong side. A handed part then comes back as its mirror image.

The projection symbol next to the title block (see Lesson 1) states the method. When the symbol is missing, the views alone can tell you.

What orthographic projection is

In orthographic projection you look at the part along one axis with parallel lines of sight, square to an imaginary plane. Each view shows two of the three dimensions at true length and hides the third. A front view shows length and height; the view from above shows length and depth; a side view shows depth and height. Every pair of adjacent views shares one dimension, which is why views are aligned. The height in the front view lines up with the height in the side view, so features can be traced across.

ISO 5456-2:1996 defines the orthographic methods and ISO 128-3:2022 governs views on drawings. Neither standard prefers one method. ISO 5456-2 defines first angle, third angle and a reference arrow method, and ISO 128-3 is neutral. Older ISO texts called first angle “method E” and third angle “method A”. ASME Y14.3-2012 (R2024) is the US standard for views, and US practice is third angle. UK and European drawings are commonly first angle, and BS 8888:2025 allows either method provided the symbol is shown.

First angle vs third angle projection: where the views go

Both methods start from the same front view. The difference is which side of it each other view is placed.

Aspect	First angle	Third angle
View from above (plan, US: top view)	Placed underneath the front view	Placed above the front view
View from the left	Placed on the right of the front view	Placed on the left of the front view
View from the right	Placed on the left of the front view	Placed on the right of the front view
Memory aid	The view is drawn on the far side, as if the part were rolled over onto the paper	The view is drawn on the near side, as if seen through a glass box
Symbol	Trapezoid left, circles right	Circles left, trapezoid right
Typical regions	Common in the UK and Europe (BS 8888 allows either)	Standard US practice (ASME Y14.3); also used on many UK projects

Figure 1 shows one part in both arrangements. It is an L-shaped block, 40 mm deep. The foot is 60 mm long and 15 mm high, with a 12 mm through hole. The upright at the left end is 20 mm thick and 40 mm high. From the left you look at the flat outer face of the upright, so the top of the foot is hidden behind it (dashed line). From the right you look at the end of the foot. The step where the foot meets the upright is a visible edge (continuous line). That single line is what lets you tell the two side views apart.

The view from above is the same picture in both methods, with the front edge of the part at the bottom of the view. What changes is whether it sits above or below the front view. The same is true of every view. A view from the left always looks the same; first angle puts it on the right, third angle on the left.

The first angle and third angle projection symbols

A symbol near the title block states the method. It is a truncated cone drawn in two views: a side view (a trapezoid) and an end view (two concentric circles). The cone is the same in both symbols; the arrangement follows the method it represents.

Aspect	First angle symbol	Third angle symbol
Layout	Trapezoid on the left, circles on the right	Circles on the left, trapezoid on the right
Narrow end of the trapezoid	Points away from the circles	Points towards the circles
Logic	Cone seen from its narrow (left) end; that view is placed on the right	Cone seen from its narrow (left) end; that view is placed on the left

How to tell first angle from third angle when the symbol is missing

Old drawings, sketches and screenshots in emails often lack the symbol. The views themselves tell you the method, provided one feature is visible from one side and hidden from the other.

Clue	What to check	Conclusion
Hidden and visible lines	In a side view, is an edge you would see from that side drawn hidden?	If the side view on the right shows what is seen from the left, it is first angle
Position of the view from above	Does the view showing the top features (holes, steps seen from above) sit above or below the front view?	Above: third angle. Below: first angle
Obvious features	A boss, slot or label that is only on one face	Find which view shows it visible and which side that view is on
Title block and origin	Company template, country of origin	Only a hint; confirm with the geometry

Choosing the front view and the number of views

The front view (the principal view) should be the one that shows the most about the part. That is usually its characteristic outline, in its functional, manufacturing or installed position, with as few hidden lines as possible. For a turned part that usually means the axis horizontal, as it sits in the lathe.

Then add only the views needed to define the part completely and without ambiguity:

Part type	Views usually needed	Reason
Turned part (shaft, pin, bush)	One, with diameter symbols	Diameters define the round form
Flat plate or sheet metal blank	One, plus thickness in a note	Thickness is constant
Prismatic machined part	Two or three	Each view adds one dimension direction
Part with an inclined face	Principal views plus an auxiliary view	Inclined faces are foreshortened in principal views

Extra views cost drafting time and give the reader more to reconcile. A view that adds only hidden lines is usually better replaced by a section, which Lesson 3 covers.

Auxiliary views and the reference arrow method

An inclined face appears foreshortened in every principal view, so its holes turn into ellipses and its true size cannot be dimensioned. An auxiliary view is projected square to that face, so the face appears at true shape. Draw only the inclined feature in the auxiliary view; the rest of the part would be distorted and adds nothing.

When a view cannot sit in its projected position, ISO 5456-2 offers the reference arrow method. An arrow on one view shows the viewing direction and carries a capital letter. The view is placed anywhere on the sheet, with the same letter above it (“A”). The arrangement no longer depends on first or third angle. That is why partial and auxiliary views on both ISO and ASME drawings are often labelled this way. Rotated views should be marked as rotated so nobody assumes a projected position.

Once the views are placed correctly, the next job is the lines inside them. Tolerances placed on those views then feed a stack-up; the tolerance stack-up worked example shows how.