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Weld Symbol Decoder (AWS A2.4)
Build a welding symbol piece by piece — weld type, side, dimensions, contour, and supplementary symbols — and read exactly what it instructs in plain English. Learn the arrow-side / other-side rule that the AWS Certified Welding Inspector exam tests hardest.
Live symbol
Below the line = arrow side. Above the line = other side. Schematic preview — not to scale.
What this symbol says
- Make a fillet weld on the ARROW side of the joint (symbol below the reference line — the side the arrow points to).
Fillet weld
A triangular weld joining two surfaces at roughly a right angle (lap, tee, or corner joint).
Exam note: The perpendicular leg of the fillet symbol is ALWAYS drawn on the left, regardless of arrow orientation. Size is to the left of the symbol; weld length is to the right.
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The Anatomy of an AWS Welding Symbol
AWS A2.4 assembles every welding symbol from the same standard elements. Once you can name each part and where it sits, any symbol on a drawing becomes readable.
Arrow Side vs. Other Side — the Rule That Trips People Up
The reference line is the horizontal backbone of every AWS A2.4 symbol, and its most important job is to encode which side of the joint gets welded. A basic weld symbol drawn below the reference line means the weld is made on the arrow side — the joint face the arrow actually points to. A symbol drawn above the line means the other side. When the same symbol appears both above and below the line, weld both sides. Because the reference line is always horizontal while the arrow can point up, down, left, or right, candidates who try to reason from the arrow's direction get it backwards; the reliable method is to read the symbol's position relative to the line.
This is the single most-tested reading rule on the CWI exam, and it is worth memorizing that AWS is the opposite of ISO 2553. Under ISO, a solid line carries the arrow-side symbol and a separate dashed identification line carries the other-side symbol, and that dashed line may sit above or below. Mixing the two conventions is a classic exam trap. Around the junction where the arrow meets the reference line you may also find a circle (weld all around) or a filled flag (field weld), and for bevel- and J-groove welds the arrow itself breaks toward the member that must be prepared.
Dimensions follow a fixed layout: weld size sits to the left of the symbol, weld length to the right, and for intermittent welds a hyphenated pitch gives the center-to-center spacing. Contour and finish symbols describe the finished weld face — flush, convex, or concave — optionally with a letter for how it is finished (C chipping, G grinding, M machining, R rolling, H hammering). Finally, the tail holds the process, filler, or WPS reference. Use the decoder above to assemble any combination and confirm your reading before you rely on it for the exam.
Frequently Asked Questions
How do you read an AWS welding symbol?
Start at the reference line — the horizontal line at the center of every symbol. A basic weld symbol placed BELOW the reference line means the weld goes on the arrow side of the joint (the side the arrow points to); a symbol ABOVE the line means the other side. Read the weld type from the symbol shape, the size from the number to the left, the length (and pitch) from the number to the right, and any process or specification from the tail.
What is the difference between arrow side and other side?
The arrow side is the joint face the arrow physically touches. The other side is the opposite face. In AWS A2.4 the location on the reference line encodes this: below the line = arrow side, above the line = other side, and symbols both above and below mean weld both sides. This is a top-tested rule — and it is the opposite convention from ISO 2553, which uses a solid line for the arrow side and a dashed identification line for the other side.
Where do the size and length of a weld go on the symbol?
The size (for a fillet weld, the leg length) is placed to the LEFT of the weld symbol. The length of the weld is placed to the RIGHT. For intermittent welds a second number after a hyphen gives the pitch — the center-to-center spacing — so '2-5' means 2-inch welds spaced 5 inches on center. Groove angle and root opening are shown near the groove symbol itself.
What do the circle and flag at the bend in the arrow mean?
A circle where the arrow meets the reference line means weld all around — the weld continues completely around the joint. A filled flag at that same junction means a field weld, made on site rather than in the shop. Both are supplementary symbols and appear at the junction, not on the weld symbol itself.
Why does the arrow sometimes bend toward one member?
For a bevel-groove or J-groove weld, only one member is prepared (cut). AWS A2.4 shows this by breaking — bending — the arrow so it points toward the member that receives the preparation. A broken arrow is a deliberate instruction, not a drafting accident, and identifying which member is prepped is commonly tested.
What goes in the tail of a welding symbol?
The tail carries the process, specification, or a reference note — for example a process abbreviation like GTAW or SMAW, a filler such as E7018, or a welding procedure specification (WPS) number. If there is no such reference, the tail is left off the symbol entirely.
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