Welding symbol builder
Assemble a symbol from its parts — the tool draws it and explains every element in words. Switching between ISO 2553 and AWS A2.4 shows the main divergence between the systems: the same picture means a different side of the joint.
What a symbol is made of
The arrow points at the joint. Where the joint is asymmetric — a single-bevel preparation, for instance — the arrow points at the member that gets prepared, and it is bent to make that unambiguous.
The reference line carries everything else. In ISO system A there are two: a continuous line and a dashed one. In AWS there is one, and the side is given by whether the symbol sits above or below it.
The elementary symbol is the shape of the weld: a triangle for a fillet, a V for a single-V butt, a square for a square butt, a half-V for a single bevel, a U or J for those preparations.
Dimensions sit either side. On the left, the size —
a5 for a 5 mm throat, z7 for a 7 mm leg. On
the right, the length and pitch.
The tail holds the process number, the WPS reference or the
quality level. A tail marked 141 means TIG, from
EN ISO 4063.
The three things that get misread
a and z. a5 is a throat of 5 mm;
z5 is a leg of 5 mm, which is a throat of only 3.5. Reading one
as the other is the most expensive mistake on this page — the conversion is in
the fillet weld
calculator.
Which side. Get the system wrong and you weld the wrong face. If a drawing shows a dashed reference line, it is ISO; if the symbol sits above or below a single line, it is AWS. The differences are set out in ISO 2553 and AWS A2.4.
The flag and the circle. Both live at the elbow of the arrow and they mean different things: circle is all-round, flag is a field weld. A drawing can carry both.
The full reading order, from arrow to tail, is in how to read welding symbols.
Frequently asked questions
Why does ISO 2553 have two lines and AWS only one?
Because the two systems answer "which side" differently. ISO 2553 system A draws a continuous line with a dashed line parallel to it: a symbol on the continuous line means the arrow side, one on the dashed line means the other side. AWS A2.4 manages with one line and uses position instead — below the line is the arrow side, above it is the other side. The second is more compact, the first is harder to misread.
What does the circle at the elbow of the line mean?
That the weld runs all the way round a closed contour: around a pipe, around the outline of a doubler plate, around a flange. Without it the weld is made only where the arrow points. A flag in the same place means something else entirely — a field weld, made on site rather than in the shop.
How is an intermittent weld written?
To the right of the symbol: number of segments, multiplication sign, segment length, and the pitch in brackets. 3×50 (100) means three 50 mm segments with 100 mm between their starting points. The size of the weld itself stays on the left of the symbol.
Can I copy the finished symbol onto a drawing?
As a teaching example, yes. As a production drawing element, no: a real drawing usually also needs the quality level to ISO 5817, the welding position and a reference to the WPS, and the drafting itself follows company conventions. This tool answers "how is this read", it does not replace design documentation.
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