First vs Third Angle Projection: Key Differences, Symbols & When to Use
First angle projection shows the object behind the picture plane; third angle places the object in front. These are standardized ways to unfold 3-D shapes into 2-D drawings.
Engineers grab whichever standard their client uses, so the same bracket drawn in Germany looks “mirrored” in the US. Mix-ups shut down production lines—machinists literally machine the wrong side.
Key Differences
First angle: viewer-object-plane order; symbol is a cone with the small end toward the front view. Third angle: viewer-plane-object order; symbol reverses the cone. Hidden detail lines may appear on opposite sides.
Which One Should You Choose?
Use First angle for ISO markets (Europe, Asia). Use Third angle for ANSI/ASME markets (US, Canada). Check the drawing title block and client spec—never guess.
Examples and Daily Life
Your IKEA shelf instructions use third angle; a German BMW gearbox print uses first angle. Both show the same holes, but one drawing “flips” the side view—easy to mis-drill if you ignore the symbol.
Can a drawing use both standards?
No. Mixing standards voids ISO/ASME compliance and risks part rejection.
How do I spot the symbol quickly?
Look for the truncated cone icon near the title block; its open end points toward the front view in third angle, away in first.
Does CAD software set the angle automatically?
No. You choose during template setup; the software only follows your selection.