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newSchoolWorks.com › VoTechWorks › Building & Construction › Welding › Blueprint Reading & Welding Symbols › Lesson 5
BLD-WELD01-07 · Lesson 5 · 14 clock hours · theory

AWS A2.4 Welding Symbols — Core Elements

Objective. Students will decode the reference line, arrow side vs. other side, tail, weld symbol, and basic supplementary symbols on any AWS A2.4 welding symbol and translate them into a written joint description.

Why Welding Symbols Matter

Every weld on a structural drawing is communicated through a standardized symbol system defined by AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination. Without a shared symbol language, fabricators, inspectors, and engineers would interpret drawings differently, leading to costly rework or dangerous failures. Mastering AWS A2.4 symbols is a foundational skill tested in the AWS SENSE and NCCER credential pathways and required on every structural jobsite governed by AWS D1.1.

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The Anatomy of a Welding Symbol

A complete welding symbol is made up of several distinct parts. Learning each part in order — from the reference line outward — is the fastest path to fluency.

Reference Line

The reference line is a horizontal line that anchors the entire symbol. Every other element of the symbol connects to or positions itself relative to this line. The reference line is always drawn horizontally regardless of the orientation of the joint in the structure.

Arrow

An arrow extends from one end of the reference line and points to the joint being welded. The arrow side of the joint — the side the arrowhead physically touches — is always called the arrow side. The opposite face of the same joint is the other side. This distinction controls where on the joint the weld is to be placed.

This rule never changes. A common memory aid: the arrow points down to the weld below the line; information above the line is on the far side.

Weld Symbol

The weld symbol (not to be confused with the complete welding symbol) is a small graphic figure placed on the reference line that identifies the type of weld. Common weld symbols include:

| Weld Type | Symbol Description |

|---|---|

| Fillet | Right triangle, perpendicular leg on the left |

| Square groove | Two vertical parallel lines |

| V-groove | An open V shape |

| Bevel groove | A single angled line |

| Plug or slot | Rectangle |

| Spot | Circle on the reference line |

| Seam | Circle with horizontal lines through it |

The exact graphic for each is shown in AWS A2.4 and on your class poster. Spend time with those reference pages; there is no substitute for repeated exposure.

Dimensions

Dimensions are written to the left of the weld symbol for size and to the right for length and pitch (for intermittent welds). For a fillet weld, the number to the left is the leg size. For groove welds, relevant numbers indicate depth of preparation and included angle.

Supplementary Symbols

Several supplementary symbols modify the basic weld symbol:

The Tail

The tail is a fork or split added to the end of the reference line opposite the arrow. It contains specification, process, or other reference information — for example, a welding procedure specification (WPS) number or a note such as "See Detail A." When no tail information is needed, the tail is omitted entirely. Its absence does not mean anything is missing; it simply means no additional data applies.

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Reading a Symbol Step by Step

Always read an AWS A2.4 welding symbol in this order:

1. Identify the reference line.

2. Note which side of the joint the arrow touches (arrow side).

3. Read the weld symbol below the line (arrow side weld) and above the line (other side weld).

4. Read dimensions — size to the left, length to the right.

5. Check for supplementary symbols (weld-all-around, field weld, contour).

6. Check the tail for process or procedure references.

7. Write the full joint description in plain English.

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Safety Note

Blueprint reading is a desk skill, but it directly affects jobsite safety. Misreading a symbol — for example, confusing arrow side with other side, or missing a weld-all-around symbol — can result in an under-welded joint that fails under load. In structural applications governed by AWS D1.1, such errors can have life-safety consequences. Always verify your interpretation against the written specification before striking an arc. If a symbol is unclear, stop and ask the engineer or supervisor — never assume.

Key terms9

Reference lineThe horizontal baseline of a welding symbol; all other symbol elements are positioned relative to it.
Arrow sideThe side of the joint that the arrow physically points to; weld information for this side is placed below the reference line.
Other sideThe face of the joint opposite the arrow; weld information for this side is placed above the reference line.
Weld symbolThe small graphic figure (triangle, V, rectangle, circle, etc.) that identifies the type of weld; one component of the larger welding symbol.
TailThe forked end of the reference line opposite the arrow; used to note specifications, processes, or procedure references. Omitted when not needed.
Weld-all-around symbolA small circle placed at the junction of the arrow and the reference line, indicating the weld is to be made continuously around the entire joint perimeter.
Field weld symbolA solid flag at the arrow-to-reference-line junction indicating the weld is to be made at the installation site rather than in the shop.
Contour symbolA line added to the face of a weld symbol specifying the required finished surface profile: flat, convex, or concave, sometimes paired with a finishing method letter.
AWS A2.4The American Welding Society standard that defines all symbols used to communicate weld and nondestructive examination requirements on engineering drawings.
In class: Instructor presents the anatomy of the AWS A2.4 welding symbol using a large laminated poster and annotated examples of groove, fillet, plug, slot, seam, and spot weld symbols; students label a blank symbol diagram. · Students work through 30 progressively complex welding symbol flash cards — each card shows one symbol; students write the full plain-English joint description on the back, then self-check against the printed answer. · In groups of three, students are given a set of five structural details and must write the correct AWS A2.4 welding symbol for each joint from the written description; groups exchange papers and grade each other's work.
Materials: AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination (current edition — student reference copies), laminated symbol poster, 30-card flash card set, structural detail drawings, NCCER Welding Level 2 Module 29201
Check: Students correctly decode at least 24 of 30 flash cards and correctly write symbols for at least 4 of 5 structural details; instructor verifies against AWS A2.4.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Blueprint Reading / AWS SENSE
1. On a welding symbol, information placed BELOW the reference line refers to a weld on the:
Blueprint Reading / AWS SENSE
2. A small circle located at the junction of the arrow and the reference line on a welding symbol means:
Blueprint Reading / NCCER
3. The TAIL of a welding symbol is used to convey:
Blueprint Reading / AWS D1.1
4. A fillet weld symbol appears ABOVE the reference line with the number 3/8 to its left. This means:
Blueprint Reading / AWS SENSE
5. Which supplementary symbol indicates that a weld is to be made at the job site rather than in the fabrication shop?
Blueprint Reading / NCCER
6. On a welding symbol, dimensions indicating weld SIZE appear to the _______ of the weld symbol, while dimensions indicating weld LENGTH appear to the _______.
Blueprint Reading / AWS D1.1
7. A welding symbol shows a V-groove symbol below the reference line with the letter 'G' next to a flat contour line. What does this combination require?
Safety / AWS D1.1 Quality
8. A welder on a structural steel project misreads the arrow side and applies the weld to the wrong face of the joint. The BEST immediate action is to:
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