AWS A2.4 Reference
Welding Symbols — AWS A2.4 Reference
A welding symbol per AWS A2.4 Section 4.5 uses a reference line, arrow, weld type graphic, dimensions, contour symbols, and a tail. AWS A2.4 Section 6.1 controls arrow-side placement, and AWS A2.4 Figure 4.3 shows standard element locations used by welders and inspectors.
How do you read a welding symbol once you know its parts? Position is the rule that matters most: symbols below the reference line apply to the arrow side of the joint, symbols above apply to the other side. This hub links the core weld symbols, supplementary symbols, NDE callouts, process designations, and worked reading guides used by fabricators, welding engineers, and CWIs.
Per AWS A2.4:2020 Section 4.5, only the horizontal reference line and arrow are required elements of a welding symbol. Figure 4.3 shows where optional elements such as weld symbols, dimensions, supplementary symbols, and tail references are placed.
Interactive Reading Guide
Explore the Symbol
Tap any chip to highlight that part of the welding symbol on the diagram. Each element is verified against AWS A2.4:2020.
Click a chip
Click any element above to highlight it on the diagram and read its definition from AWS A2.4:2020.
Quick Reference
| You see… | It means… |
|---|---|
| Below ref line | Weld on the arrow side |
| Above ref line | Weld on the other side |
| Both sides of ref line | Weld on both sides |
| Open circle at junction | Weld all around the joint perimeter |
| Solid flag at junction | Field weld (made on site, not in shop) |
| Number left of weld symbol | Size (leg length for fillet; D(S) for groove) |
| Numbers right (e.g., 3–12) | Length–pitch for intermittent welds |
| Tail (V-shape opposite arrow) | Process / WPS reference / spec note |
Can't find your symbol? Ask Flux
Print-Ready Chart →
Single-page reference for shop floor use
If the welder can't read the symbol, everything downstream breaks — the WPS match, the fit-up, the inspection acceptance criteria. Symbol literacy is the first checkpoint, not the last.
— Field perspective, structural fabrication QC
Go Deeper
Joint Types and Drawing Lines
The interactive above covers symbol anatomy. The full Blueprint Reading Guide adds joint types per AWS A2.4:2020 Figure 5.1 and the 10 engineering drawing line conventions per ASME Y14.2-2014 — the “alphabet of lines” that carries the rest of a welding drawing’s meaning.
△ Blueprint Reading Guide — Joint Types + Drawing Lines Go deeper than anatomy. 5 joint types per AWS A2.4 Figure 5.1 (butt, corner, T, lap, parallel) and the 10 engineering drawing line conventions per ASME Y14.2-2014 — the alphabet that carries the rest of a welding drawing’s meaning.Weld Types
Core Welding And Supplementary Symbols — AWS A2.4
Each symbol below maps to a welding procedure specification (WPS) that defines how the weld is made, backed by a procedure qualification record (PQR) proving the procedure produces sound results. Standard joints may follow prequalified WPS rules that eliminate qualification testing, and a certified welding inspector (CWI) verifies the finished work against code.
The chart below separates weld type symbols, supplementary symbols, and related drawing-reading pages. Start with the fillet weld symbol if you need the most common structural callout, then move to groove welds, plug/slot welds, NDE symbols, process designations, and the printable charts when you need a shop-floor reference.
Fillet
Right-triangle symbol. Most common weld type in structural steel.
Groove Welds
Hub page for all groove weld types: V, bevel, square, J, U, flare.
V-Groove
V-shape symbol. CJP or PJP groove weld.
Bevel Groove
Angled line. One member prepared, broken arrow points to it.
J-Groove
J-curve symbol. Perpendicular leg always on the left.
Square Groove
Parallel lines. Butt joint with square edge prep.
Plug Weld
Open rectangle with diameter. Round hole filled with weld metal.
Slot Weld
Open rectangle with width + length. Elongated hole filled with weld metal.
Spot Weld
Plain circle. Resistance or arc spot weld.
Seam Weld
Circle with horizontal line. Resistance or arc seam weld.
Surfacing
Wavy line. Hardfacing, buildup, or cladding on base metal surface.
Edge Weld
Bracket shape. Flanged butt and flanged corner joints.
Backing / Back
Open semicircle. Sequence determines backing vs back weld.
Melt-Through
Filled semicircle. CJP with visible root reinforcement from one side.
Field Weld
Filled flag at junction. Weld made on-site, not in shop.
Weld-All-Around
Circle at arrow junction. Continuous peripheral weld.
Stitch Weld
Intermittent fillet weld. Stitch weld symbol uses length-pitch notation per A2.4 §8.4.
U-Groove
U-curve symbol. Both members prepped. Root radius in cross-section detail only.
Flare-V Groove
Y-shape. Two curved members in contact. No machining — groove shape is inherent.
Flare-Bevel Groove
C-shape. Curved member to flat surface. Broken arrow points to curved member.
Stud Weld
Circle-X symbol. Arrow-side only. Size left, pitch right, count in parens below.
Quick Reference
Weld Symbol Element Reference
| Element | Location | Meaning |
|---|---|---|
| Weld symbol | Above or below reference line | Weld type — fillet triangle, groove V, plug circle, etc. Below = arrow side, above = other side. |
| Arrow side | Below reference line | Same side as arrow — weld on the surface the arrow points to |
| Other side | Above reference line | Opposite side from arrow — weld on far face of joint |
| Both sides | Both sides of line | Weld both sides — same symbol above and below reference line |
| Weld size | Left of weld symbol | Leg size (fillet) or groove depth (groove welds), in inches or mm |
| Weld length | Right of weld symbol | Length of weld in inches or mm. Omitted = full length. |
| Pitch | Right of symbol, as length-pitch (e.g. 3-12) | Center-to-center spacing of intermittent welds — pitch follows the dash after weld length |
| Contour symbol | Above/below weld symbol | Flush (straight line), Convex (outward arc), Concave (inward arc) — desired weld face profile |
| Finishing symbol | Adjacent to contour symbol | G (grind), M (machine), C (chip), H (hammer), P (planish), R (roll), U (unspecified) — per A2.4 §6.13 |
| Tail | Right end of reference line | Specification, process, or note — e.g. SMAW, AWS D1.1, or WPS number |
| Weld-all-around | Circle at arrow junction | Weld completely around the joint — all sides, no breaks |
| Field weld | Filled flag at reference line | Weld on-site during erection, not in the fabrication shop |
| CJP | In tail or note | Complete Joint Penetration — weld fuses full thickness of joint |
| PJP | In tail or note | Partial Joint Penetration — groove depth less than full thickness |
"Welding symbols are the universal language between the engineer at the desk and the welder in the field — without them, every joint is a conversation."
— Widely cited in structural steel fabrication training, reflecting AWS A2.4 standard practice
Reference & Study
Beyond Weld Types
NDE callouts, process codes, and CWI exam prep — essential knowledge for reading and interpreting engineering drawings.
NDE Symbols
RT, UT, MT, PT, VT, ET — examination callouts on drawings.
CWI Practice Test
198 questions across 18 categories. Track your score.
Quick Diagnostic
Fast symbol-reading check for arrow side, tail, field welds, and NDE callouts.
Process Codes
SMAW, GMAW, FCAW-S — all 136 AWS process designations.
ISO 2553 Comparison
System A dashed line, a/z modifiers, arrow-side flip.
Contour & Finishing
Flush, convex, concave + 7 finishing letters (G, M, C, H, P, R, U).
Multiple Ref Lines
Sequence of operations, back vs backing weld order.
Complete A2.4 Reference
All symbols, NDE, processes — printable multi-page reference.
Print-Ready Chart
Single-page quick lookup — basic weld and supplementary symbols for A4 or letter.
Common Questions
Weld Symbol FAQ
Related Tools
What is a weld symbol?
A weld symbol is the small graphic element that identifies the weld type, such as a fillet triangle or groove symbol. A welding symbol is the complete drawing notation. In AWS A2.4, only the horizontal reference line and arrow are required; optional elements such as weld symbols, dimensions, supplementary symbols, and a tail are placed in the standard locations shown in Figure 4.3. That means a drawing may legally use notes, details, specifications, codes, or other drawings to supply information that is not written directly inside the symbol. North American drawings normally use AWS A2.4, while international projects may use ISO 2553, so always confirm the drawing standard before interpreting arrow-side and other-side placement.
What is the difference between a weld symbol and a welding symbol?
A weld symbol refers specifically to the small graphic element that indicates the weld type — for example, a right triangle for a fillet weld, a V-shape for a V-groove weld, or a rectangle for a plug weld. It is one component of the larger notation. A welding symbol refers to the complete assembly of elements that together convey the full welding instruction: the reference line, arrow, weld symbol, dimensions (size and length), supplementary symbols (weld-all-around circle, field weld flag, contour and finishing designators), and the optional tail containing process codes, specification references, or WPS numbers. AWS A2.4 makes this distinction explicit in its terminology section. In practice, many welders and engineers use the terms interchangeably, but on CWI exams and in formal specification writing, the distinction matters — a "weld symbol" is just the type indicator, while a "welding symbol" is the entire graphical instruction on the drawing.
What does arrow side and other side mean?
The reference line is the horizontal backbone of every welding symbol, and it divides the symbol into two zones that determine weld placement. The arrow side is indicated by placing the weld symbol below the reference line — this means the weld goes on the same side of the joint that the arrow physically points to. The other side is indicated by placing the weld symbol above the reference line — this means the weld goes on the opposite side of the joint from where the arrow points. When weld symbols appear on both sides of the reference line, the welder must weld both sides of the joint. This convention is defined in AWS A2.4 sections 6.1 and 6.2. Note that ISO 2553 uses a different convention — in System A, a dashed identification line indicates the other side rather than using position above or below the reference line — which is a common source of confusion on international projects. Always confirm which standard the drawing references before interpreting arrow-side versus other-side placement.
What is the circle on a weld symbol?
A small circle placed at the junction where the reference line meets the arrow is the weld-all-around symbol. It instructs the welder to make the weld continuously around the entire perimeter of the joint without any breaks or gaps. Common applications include tube-to-plate connections where all four sides of a rectangular tube must be welded to a baseplate, circular pipe penetrations through a plate, and gusset plate attachments. Per AWS A2.4, the circle is always placed at the reference line and arrow junction — it does not appear anywhere else on the symbol. The weld-all-around symbol can be combined with any weld type symbol (fillet, groove, etc.) and with the field weld flag. When you see both a weld-all-around circle and a field weld flag at the junction, it means the entire perimeter weld must be completed in the field during erection rather than in the shop.
What does the flag on a weld symbol mean?
A filled triangle (flag) at the junction of the reference line and arrow is the field weld symbol. It indicates the weld must be made in the field during erection — not in the fabrication shop. This distinction is critical for structural steel projects because shop welds and field welds are subject to different quality control procedures, different inspection requirements, and often different welding processes. Shop welds are typically made under controlled conditions with SAW or GMAW, while field welds often use SMAW or FCAW due to access constraints and outdoor conditions. Per A2.4 §6.9, the field weld flag may point in either direction. On structural steel erection drawings, field welds are commonly fillet welds at beam-to-column moment connections, splice plates, and bracing connections. CWIs performing field inspection specifically look for the field weld flag to identify which joints require on-site verification and documentation.
What does G mean on a weld symbol?
The letter G adjacent to a contour symbol on a welding symbol means grind — the completed weld face must be ground to achieve the contour specified by the accompanying contour symbol. The contour symbol can indicate flush (straight line), convex (outward arc), or concave (inward arc) profile. Together, a flush contour symbol plus the letter G means "grind this weld flush with the base metal surface." Other finishing designators defined in AWS A2.4:2020 include M for machining, C for chipping, H for hammering (peening), P for planishing, R for rolling, and U for unspecified finishing method. The finishing designator appears adjacent to the contour symbol, above or below the weld symbol depending on which side of the joint the finish applies to. Grinding is the most commonly specified finishing method in structural steel work, particularly for CJP groove welds at moment connections where a flush surface is required for proper fit-up of connecting elements. See full explanation of the G finishing symbol.
What is the difference between AWS A2.4 and ISO 2553?
AWS A2.4 and ISO 2553 both define welding symbols for engineering drawings, but they use opposite conventions for indicating which side of the joint is welded. In AWS A2.4, the weld symbol below the reference line indicates the arrow side of the joint, and above indicates the other side. ISO 2553 uses a different mechanism — System A places the symbol on a dual reference line (continuous = arrow side, dashed = other side), while System B uses position-above/below identically to AWS A2.4 — in the identification system (formerly System A), the symbol on the side of the reference line with the dashed line indicates the other side. This reversal is the single most important difference and the most common source of confusion on international projects. Always confirm which standard a drawing references before interpreting arrow-side versus other-side placement. Other differences include: ISO uses different size shortcodes (a for throat, z for leg, s for depth), ISO has System A and System B variants, and some supplementary symbol conventions differ.
Related Reference