01 / Foundation
A symbol is a structured instruction.
A welding drawing should tell fabrication personnel what weld is required, where it belongs, how large or long it is, and what additional requirements control it.
A weld symbol is the graphical mark for a weld type, such as a fillet or V-groove. A welding symbol is the complete assembly: reference line, arrow, weld symbol, dimensions, supplementary symbols, and tail when those elements are needed.
AWS A2.4 states that only the reference line and arrow are required elements of the complete welding symbol. Everything else is included when it communicates an actual requirement. Missing information may instead be provided by notes, details, specifications, codes, or other drawings.
Illustrative Xeon NC diagram. The example is built to teach element locations; it is not a production weld specification.
The symbol communicates the requirement. It does not design the joint for you.AWS A2.4 explains how to express welding information; it does not set the engineering design, acceptance criteria, welding procedure, qualification, or safety program.
02 / Location significance
Below is arrow side. Above is other side.
The reference line works like an address. The weld symbol's position relative to that line tells the welder which side of the joint receives the weld.
Arrow side
Symbol below
The weld is made on the side of the joint to which the arrow points.
Other side
Symbol above
The weld is made on the side opposite the arrow side of the joint.
Both sides
Symbols above & below
The specified weld is required on both sides where that application is permitted.
When the arrow breaks
For bevel- and J-groove applications where one member must receive the edge preparation, a break in the arrow identifies the member to be prepared. Do not treat arrow direction as decoration; it can carry manufacturing meaning.
03 / Basic weld symbols
Start with the weld family.
Use the filters to compare the core symbol families. The diagrams show the weld mark on a reference line; real instructions may add side placement, size, length, pitch, contour, finish, process, or other requirements.
Sheet & plate
Fillet
Triangular weld commonly used at T-, lap-, and corner-joint intersections. Size normally appears to the left; length and pitch appear to the right.
Groove
Square groove
Parallel edges with no bevel symbolized. Root opening, weld size, and penetration requirements still have to be specified where needed.
Groove
V-groove
Both members are prepared to form a V. Groove angle, root opening, depth of preparation, and weld size may accompany the mark.
Groove
Bevel groove
One member is prepared and the other remains square. A broken arrow identifies which member is to be beveled when necessary.
Groove
U-groove
Curved preparation on both members. Commonly considered where a prepared groove can reduce weld-metal volume on thicker material.
Groove
J-groove
One member receives a curved J preparation while the mating member remains square. Arrow-member significance matters.
Groove
Flare-V groove
Used where two rounded surfaces create the groove, such as adjacent round members or formed flanges.
Groove
Flare-bevel groove
Used where one rounded member meets a planar member. The actual joint configuration and weld-size basis need careful review.
Sheet & plate
Plug / slot
Weld metal fills a circular or elongated opening in one member to join it to another. Size, number, pitch, filling depth, and slot length may be specified.
Spot & projection
Spot / projection
A circular symbol identifies discrete weld locations. Size belongs to the left; number, pitch, extent, and process information may also control the requirement.
Resistance / arc seam
Seam
A linear weld produced along the joint rather than at isolated spots. Size, length, pitch, number, and process can be added as required.
Special
Stud
Specifies studs welded to a surface. Stud size, number, pitch, and process information belong in their standard locations.
Sheet & plate
Edge
Joins adjacent edges, including flanged arrangements. Size, length, intermittent pattern, and melt-through requirements may be specified.
Special
Surfacing
Deposits weld metal on a surface for buildup, restoration, corrosion resistance, or wear service rather than joining two members.
Special
Back / backing
The same mark serves two meanings; sequence or context distinguishes a back weld from a backing weld. Multiple reference lines can show operation sequence.
04 / Supplementary symbols
These marks modify the instruction.
A basic weld symbol says what kind of weld. Supplementary symbols add extent, location, contour, penetration, backing, or special execution requirements.
Weld all around
A circle at the arrow/reference-line junction means the specified weld continues around the joint identified by the arrow—not every joint on the part.
Field weld
A flag at the arrow/reference-line junction identifies welding performed at the field or installation location rather than the normal shop location.
Contour
Flush/flat, convex, or concave contour marks establish the required final profile. Under A2.4:2020, “flat” applies to fillets; “flush” applies to other welds.
Finish method
A letter can specify how contour is achieved: common drawing conventions include C for chipping, G for grinding, M for machining, R for rolling, H for hammering, and U for unspecified.
Melt-through
Calls for visible root reinforcement on the opposite side of a joint welded from one side. Reinforcement height may be dimensioned.
Backing / spacer
A rectangle indicates backing or a spacer at the joint. An R can require backing removal. Material and geometry belong in the tail, note, or detail.
Complete joint penetration
The CJP supplementary mark requires complete joint penetration regardless of the groove form used to achieve the qualified joint.
Consumable insert
Identifies a consumable insert at the joint root. Insert class or specification is placed in the tail or otherwise referenced.
Multiple reference lines
Lines nearest the arrow describe the first operation; additional lines describe later operations or sequences.
05 / Numbers and placement
The mark says what. The numbers say how much.
Dimension placement is standardized so the reader can scan a symbol in a repeatable order. Interpret every value with the drawing's declared unit system and governing requirements.
| Location | Typical information | Reading rule |
|---|---|---|
| Left of weld symbol | Fillet size; groove depth and/or weld size; plug/slot size; spot, seam, stud, or edge size | The exact meaning depends on the weld family and whether values appear in parentheses. |
| Right of weld symbol | Length, followed by pitch when intermittent; slot length; seam length or pitch | A dash commonly separates length from pitch, such as 50–150. |
| Inside groove symbol | Root opening or depth of filling | Do not infer a root opening from the sketch alone; read the placed value or joint detail. |
| Above groove symbol | Included groove angle; countersink angle for plug welds | Angle belongs with joint preparation, not weld length. |
| Near supplementary mark | Contour finish letter or root-reinforcement dimension | Contour and finish are separate ideas: shape first, method second when required. |
| In the tail | Process, procedure, specification, electrode, backing, inspection, or other references | The tail may be omitted when it carries no information. |
Units do not live inside AWS A2.4 by default.The standard does not require one measurement system. Confirm whether the drawing uses inches, millimeters, or another declared basis before interpreting any number.
06 / Joint types
Joint type is geometry. Weld type is instruction.
The five foundational joint types describe how the members are arranged before welding. One joint type can support multiple weld types depending on load path, thickness, access, process, code, and design.
01 / Butt
Butt joint
Two members aligned in approximately the same plane with edges meeting. Common choices include square, V, bevel, U, J, and flare groove configurations.
02 / Corner
Corner joint
Members meet at or near their edges to form an L or corner. Fillet, groove, and edge weld arrangements are possible depending on the edge preparation and access.
03 / T
T-joint
One member intersects the surface of another, usually near 90 degrees. Fillet welds are common; groove welds may be designed when penetration through the member thickness is needed.
04 / Lap
Lap joint
Members overlap one another. Fillet welds at accessible overlap edges, plug or slot welds through one member, and spot or seam welds are common approaches.
05 / Edge
Edge joint
Adjacent member edges are placed together and welded along the edge. This family includes edge welds and flanged arrangements often seen in sheet metal.
Do not choose a weld from the joint name alone.Loads, base metal, thickness, service environment, fatigue, access, distortion, inspection, and the governing code all influence the engineered weld requirement.
07 / Reading complete instructions
Decode in the same order every time.
Start at the arrow, establish the side, identify the weld family, read dimensions, then add supplementary and tail requirements.
6 mm intermittent fillet, arrow sideThe triangle below the line selects the arrow side. The 6 at left is fillet size. The 50–150 to the right calls for 50 mm weld segments at 150 mm pitch, assuming the drawing is dimensioned in millimeters.
Both-side fillet, all around the identified jointTriangles above and below the reference line call for fillets on both sides. The circle applies the specified weld continuously around the joint identified by the arrow.
Arrow-side V-groove with flush contour, grinding finishThe V below the line identifies the arrow-side groove weld. The straight contour and G finish letter add the final-profile and finishing-method requirement. Joint preparation and weld size still require their placed dimensions or detail.
Seven-step drawing review
01
Find the arrow target.Confirm which physical joint or joint line is identified.
02
Establish arrow side and other side.Use symbol placement above and below the reference line.
03
Identify the weld family.Fillet, groove, plug/slot, spot, seam, stud, edge, surfacing, or another defined application.
04
Read left-side dimensions.Determine size, depth, or the family-specific quantity being specified.
05
Read right-side dimensions.Check length, pitch, number, or extent as applicable.
06
Add supplementary requirements.All-around, field weld, contour, finish, backing, melt-through, CJP, or sequence.
07
Follow the tail and governing documents.Resolve process, procedure, code, inspection, material, and acceptance criteria before release.
08 / Frequently asked questions
Welding-symbol FAQs.
What is the difference between a weld symbol and a welding symbol?
A weld symbol is the graphical mark identifying a weld type. A welding symbol is the complete instruction, which may include the arrow, reference line, weld symbol, dimensions, supplementary symbols, and tail.
What do symbols below and above the reference line mean?
Under the AWS system, a weld symbol below the reference line applies to the arrow side. A symbol above the line applies to the other side. Symbols on both sides call for welding on both sides where permitted.
What are the five foundational welding joint types?
Butt, corner, T, lap, and edge joints. Joint type describes member arrangement; it does not by itself establish weld type, size, penetration, process, or acceptance.
Does a weld-all-around symbol mean weld everything on the part?
No. It means the specified weld continues around the joint identified by the arrow. The drawing must still identify that joint and its extent clearly.
Can the tail be left off a welding symbol?
Yes. The tail is optional when it carries no process, specification, procedure, or other reference. The arrow and reference line are the required foundation.
Can Xeon NC review my welded-part CAD and drawing?
Yes. Upload the supported CAD and drawing, then request applications-engineering review for joint access, tabs and slots, clearances, tolerances, material, finish, and manufacturing requirements.
Standards and references
- American Welding Society — AWS A2.4:2020, Standard Symbols for Welding, Brazing, and Nondestructive Examination
- American Welding Society — AWS A3.0M/A3.0:2025, Standard Welding Terms and Definitions
- American Welding Society — Understanding Welding Symbols course overview
This Xeon NC guide is an educational overview, not the official standard, a welding procedure specification, an engineering design, or a substitute for the contract documents. Verify the invoked edition and all project requirements.