Resistance spot and seam weld symbols tell a fabricator where a weld belongs and how its size, spacing, length, quantity, contour, and related requirements are specified. The details are compact, so one misplaced dimension can change the meaning. This guide follows the AWS A2.4:2020 convention and explains the symbols in a practical reading order.
Quick Answer
Under AWS A2.4:2020, spot weld size (diameter) and seam weld size (width) go to the left of the symbol. Spot-weld pitch goes to the right; seam length and, for intermittent seams, pitch go to the right. Strength is no longer placed on the left—it belongs in a tail note.
Key Takeaways
- A spot weld uses the spot-weld circle symbol; a seam weld uses the seam-weld symbol made from two parallel lines.
- Spot weld diameter and seam weld width are specified to the left of the weld symbol under AWS A2.4:2020.
- Spot-weld pitch is the center-to-center distance between spots in a straight line and is placed to the right.
- For intermittent seam welds, the right-side notation can show segment length followed by pitch.
- AWS A2.4:2020 changed the strength rule: required spot or seam weld strength is specified as a note in the tail rather than as the left-side value.
- Always confirm whether the drawing follows AWS A2.4, ISO 2553, or another governing specification before interpreting its symbols.
At a Glance
| Time Required | Usually 1–5 minutes to decode a single symbol once the governing standard is known |
| Difficulty | Beginner to intermediate |
| Tools Needed | Issued drawing, drawing notes/legend, and the applicable AWS or ISO standard |
| Cost | No added cost to read an issued drawing; full standards may require purchased or employer-provided access |
Warning: Do not fabricate or accept a production weld from an internet example alone. Use the issued drawing, contract documents, applicable welding code or standard, approved procedure, and instructions from qualified personnel. Resistance-welding machines also present pinch, electrical, heat, and flying-spark hazards.
Resistance Spot and Seam Weld Symbols Explained
Resistance spot and seam weld symbols are part of the complete welding symbol used on an engineering drawing. Under AWS terminology, the weld symbol is the small graphical mark that identifies the weld type, while the complete welding symbol can also include the arrow, reference line, tail, dimensions, quantity, contour symbols, and other information.
The current AWS reference for this notation is AWS A2.4:2020, Standard Symbols for Welding, Brazing, and Nondestructive Examination. AWS states that the standard provides a method for conveying welding, brazing, and nondestructive-examination requirements through symbols.
One important AWS A2.4:2020 change affects both spot and seam welds: a value to the left of the symbol now identifies weld size only. Required strength is specified as a note in the tail.
A resistance spot weld is commonly identified with the spot-weld circle symbol. A resistance seam weld uses the seam-weld symbol formed by two parallel lines. Dimensions placed around those symbols tell the reader how large the weld must be and, where applicable, how the welds repeat along the joint.
These drawing requirements are separate from process-selection questions such as choosing common welding consumables. A weld symbol communicates design requirements; it does not by itself choose the machine, electrode, procedure variables, or operator technique.
Which Welding Symbol Standard Are You Reading?
Check the drawing title block, general notes, specification, contract documents, or welding-symbol legend before decoding individual symbols. This article uses the AWS A2.4:2020 system.
International drawings may instead follow ISO 2553:2019. ISO recognizes different approaches to arrow-side and other-side representation, so an AWS explanation should not automatically be applied to an ISO drawing. As of September 2026, ISO 2553:2019 remains the published edition, while ISO/DIS 2553 is a draft revision under development.
Pro Tip: Identify the governing standard before reading dimensions. A familiar-looking symbol can be interpreted incorrectly when AWS and ISO conventions are mixed.
How to Read a Resistance Spot Weld Symbol
Start with the spot-weld circle and its position relative to the reference line. Under AWS A2.4:2020, spot-weld symbols can have arrow-side member significance, other-side member significance, or no side significance.
- Below the reference line: used when the symbol needs to identify the arrow-side member.
- Above the reference line: used when the symbol needs to identify the other-side member.
- Centered on the reference line: used when the welding process has no arrow-side or other-side significance.
Dimensions belong on the same side of the reference line as the symbol. If the symbol is centered because there is no side significance, the dimensions can be presented with that centered arrangement.
The weld process can be identified in the tail of the welding symbol. For resistance spot welding, the process designator RSW may appear there. The tail is also where AWS A2.4:2020 places a required strength value when strength, rather than weld size, controls the requirement.
Machine capability remains a separate issue. For example, duty cycle matters when selecting and operating welding equipment, but it is not a dimension encoded by a resistance spot-weld symbol.
Spot Weld Size, Pitch, and Spacing
For an AWS-style spot weld, read the key fields in this order: size on the left, pitch on the right, quantity in parentheses when specified, and process or strength information in the tail when required.
| Item | AWS Location | Meaning |
|---|---|---|
| Spot weld size | Left of symbol | Required weld diameter |
| Pitch | Right of symbol | Center-to-center distance between spot welds in a straight line |
| Number of welds | In parentheses near the symbol | Specified quantity of spot welds |
| Strength | Note in the tail under AWS A2.4:2020 | Required force/strength when strength is used instead of size |
| Process | Tail | Identifies the required welding process, such as RSW |
The word pitch already describes center-to-center spacing for spot welds arranged in a straight line. If a group has a different pattern, random locations, or a limited extent, the drawing may need centerlines, area limits, or additional dimensions rather than a second generic “spacing” value.
Do not choose a weld diameter from machine capability or material thickness alone. The drawing requirement comes first. Equipment-selection considerations discussed in guides to weld specifications and beginner equipment are separate from the dimensions specified by the engineering drawing.
Spot Weld Reading Example
Suppose an AWS-style spot-weld callout shows a size of 6 to the left of the circle, a pitch of 40 to the right, and (5) as the quantity, with RSW in the tail. If the drawing uses millimetres, that means five resistance spot welds, each with a specified 6 mm weld diameter, arranged at 40 mm center-to-center pitch. The drawing must still be checked for the exact location and extent of that five-weld group.
Note: Never assume drawing units from an isolated symbol. Confirm the drawing’s unit convention before interpreting a number as millimetres, inches, newtons, or another unit.
Spot Weld Count and Flush Symbols
A definite number of spot welds is shown in parentheses. Under AWS A2.4:2020, the quantity belongs on the same side of the reference line as the spot-weld symbol. Where the symbol is centered because no side significance applies, the quantity can be placed above or below as appropriate.
Spot-weld quantity should not be confused with size or pitch. A value in parentheses answers how many; the left-side dimension answers how large; and the right-side pitch answers how far apart the repeated welds are.
The specified symbol still does not prove that a particular machine has adequate material-thickness capacity. Procedure qualification, machine capability, electrode force, current, time, material stack-up, and acceptance criteria are separate production considerations.
Spot Weld Count
When the designer requires an exact number of spot welds, the parenthetical quantity gives that total. For grouped spot welds, the drawing may also use intersecting centerlines or a clearly defined area to show where the welds belong.
If spot welding covers less than the available joint length, the required extent should be dimensioned on the drawing. Quantity alone does not necessarily tell the fabricator where the first and last welds must fall.
Flush Symbol Placement
A flush contour symbol tells the fabricator that the exposed weld surface must meet the specified flush contour. It should not be read as an automatic instruction to grind, machine, or polish the weld by a particular method unless the welding symbol or drawing separately specifies that finishing method.
This distinction matters because AWS A2.4:2020 changed its contour rules so that a required contour can be achieved by an appropriate method unless a particular postweld finishing method is designated.
How to Read a Resistance Seam Weld Symbol
A resistance seam weld uses the seam-weld symbol, shown as two parallel lines. As with spot welds, first check whether the symbol is above, below, or centered on the reference line.
- Below: arrow-side member significance where applicable.
- Above: other-side member significance where applicable.
- Centered: no arrow-side or other-side significance.
Next read the size to the left and the length-related information to the right. Under AWS A2.4:2020, seam weld size means weld width. If strength rather than width is specified, the strength is given as a note in the tail instead of being placed as the left-side dimension.
The process reference can also appear in the tail. RSEW is the standard process abbreviation for resistance seam welding.
Symbol reading and actual welding processes and equipment remain separate subjects. The drawing defines the requirement; the qualified procedure and production setup determine how that requirement is achieved.
Seam Weld Symbol Basics
Read an AWS seam-weld symbol in a consistent order:
- Identify the seam-weld symbol and its side significance.
- Read the weld width to the left if size is specified.
- Read seam length to the right if a specific length is required.
- For an intermittent seam, read segment length and pitch on the right.
- Check parentheses for a specified number of seam welds.
- Check the tail for process and any specified strength requirement.
- Check supplementary symbols for contour or other requirements.
If the seam weld extends the full distance between abrupt changes in the direction of welding, AWS permits the length dimension to be omitted. If it covers only part of that available distance, the drawing must make the required extent clear.
Reading Size and Pitch
The left-side seam-weld dimension specifies weld width. For an intermittent seam, pitch is the center-to-center distance between weld segments.
The right-side intermittent notation is normally read as length-pitch. For example, a notation such as 25-75 on a metric drawing would indicate 25 mm weld segments on 75 mm centers, provided those are the drawing’s established units.
Do not substitute “diameter” for seam-weld width. Diameter belongs to spot-weld size; width is the relevant AWS size term for a seam weld.
Seam Weld Length, Pitch, and Intermittent Runs
The right side of the seam-weld symbol controls length-related information. A continuous seam that requires a stated length uses that length to the right of the symbol. An intermittent seam combines segment length and pitch so the fabricator can see both how long each welded segment is and how far apart the segment centers are.
Under AWS A2.4:2020, the pitch of intermittent seam welds is measured between the centers of the weld segments. Unless the drawing indicates otherwise, intermittent seam length and pitch are interpreted parallel to the weld axis.
Continuous vs. Intermittent Seam Example
If the drawing calls for a seam width of 5 on the left and a length of 200 on the right, the specified seam is 5 units wide and 200 units long under the drawing’s unit system. If the right side instead reads 25-75, it describes intermittent segments 25 units long at 75-unit pitch.
A number in parentheses can additionally specify how many seam welds or segments are required where the standard’s quantity convention applies.
Personal protective equipment is still necessary even though PPE is not encoded by the weld symbol. Topics such as helmet optical clarity ratings concern safe equipment selection rather than seam-weld dimensioning.
Flush Contours and Other Seam Weld Details
A flush contour symbol added to a seam-weld callout requires the specified weld face to have an approximately flush contour. The contour symbol describes the required final shape; it does not by itself prescribe a specific finishing process.
If a drawing requires grinding, machining, or another particular finishing operation, read that requirement separately from the contour symbol. This prevents two common errors: assuming every flush weld must be ground, or assuming a visually flat weld automatically meets a specified finish requirement.
The contour symbol controls the required weld profile. A specific finishing method is a separate instruction unless the drawing explicitly combines the two.
Shop setup also remains outside the symbol itself. A stable work surface and appropriate fixtures can improve production control, but features discussed in guides to welding tables do not change the engineering meaning of a seam-weld callout.
What Spot and Seam Weld Symbols Do Not Tell You
A welding symbol communicates design and drawing requirements, but it is not a complete welding procedure. Unless the drawing, code, WPS, or other governing document adds the information, the symbol alone does not select:
- machine settings or current/time schedules;
- electrode force or electrode condition;
- material preparation;
- inspection and acceptance criteria;
- operator qualification;
- PPE and guarding;
- arc-welding filler metal or shielding gas for unrelated processes.
For example, a 75/25 shielding-gas mix may be relevant to certain GMAW applications, but it has nothing to do with how an AWS resistance spot- or seam-weld symbol’s diameter, width, pitch, or length is read.
Common Mistakes in Weld Symbol Reading
- Using an older strength convention. Under AWS A2.4:2020, the left-side value for spot and seam welds represents size. Required strength belongs in a tail note.
- Assuming the symbol must always be centered. Centering indicates no side significance; above/below placement can identify the applicable member when side significance exists.
- Confusing pitch with edge-to-edge gap. Spot-weld pitch and intermittent seam pitch are center-to-center measurements.
- Reading spot diameter as seam width, or vice versa. Spot size is diameter; seam size is width.
- Treating parentheses as a dimension. Parentheses can identify the specified number of spot or seam welds.
- Assuming a flush contour specifies grinding. The contour and the finishing method are separate requirements unless both are specified.
- Ignoring the drawing’s governing standard. AWS and ISO systems should not be mixed casually.
- Guessing omitted information. If the required location, unit system, process, extent, or acceptance requirement is unclear, resolve it through the drawing/specification process rather than inventing a value.
Safety When Working From Resistance-Weld Drawings
Correct symbol reading does not replace machine safety. OSHA 29 CFR 1910.255 addresses resistance-welding equipment and includes requirements involving qualified operators, electrical controls, machine guarding, foot-switch protection, emergency stops, and protection from flying sparks.
OSHA’s general welding requirements also call for appropriate eye or face protection for resistance-welding operations. See 29 CFR 1910.252 for related welding safety provisions.
Before production, verify the drawing revision, applicable code, approved welding procedure, inspection requirements, material stack-up, and machine setup. A correctly decoded symbol is only one part of producing an acceptable weld.
Frequently Asked Questions
How do you interpret weld symbols?
First identify the governing standard. Then read the arrow and reference line, identify the weld symbol, determine arrow-side or other-side significance, and read dimensions in their standard locations. Finally, check quantity, supplementary symbols, the tail, drawing notes, and any code or specification referenced by the drawing.
What is the symbol for a spot weld?
Under AWS A2.4, the spot-weld symbol is a circle. Its position relative to the reference line can identify arrow-side, other-side, or no-side significance. Weld diameter is specified to the left, pitch to the right for spots in a straight line, and a required quantity is shown in parentheses. The process, such as RSW, can be identified in the tail.
What are the different types of seam weld symbols?
AWS uses the basic seam-weld symbol and adds dimensions or supplementary information to communicate the requirement. A seam can be continuous or intermittent; its size, length, pitch, quantity, contour, process, and strength requirements are conveyed by the surrounding dimensions, symbols, notes, and tail rather than by inventing a separate basic symbol for every variation.
Where does weld strength go on a spot or seam weld symbol?
Under AWS A2.4:2020, the left-side value identifies spot-weld diameter or seam-weld width. When strength is the specified requirement, the strength is given as a note in the tail of the welding symbol.
What does pitch mean on a resistance weld symbol?
Pitch is a center-to-center measurement. For spot welds in a straight line, it is the center-to-center distance between adjacent spots. For intermittent seam welds, it is the center-to-center distance between seam-weld segments.
What do 1F, 2F, 3F, and 4F mean in welding?
They are fillet-weld position designations: 1F is flat, 2F is horizontal, 3F is vertical, and 4F is overhead. These position codes are used in welding qualification and procedure contexts; they are not alternative names for resistance spot- or seam-weld symbols.
Sources
- American Welding Society — AWS A2.4:2020 — governing AWS reference for welding-symbol construction and interpretation.
- AWS A2.4:2020 official preview — confirms the 2020 change that spot- and seam-weld strength is placed in a tail note rather than as the left-side dimension.
- ISO 2553:2019 — international standard for symbolic representation of welded joints on technical drawings.
- ISO/DIS 2553 — 2026 draft revision under development.
- OSHA 29 CFR 1910.255 — Resistance welding — resistance-welding equipment, operator, guarding, control, and spark-protection requirements.
- OSHA 29 CFR 1910.252 — General welding requirements — related eye, face, and welding safety requirements.
Conclusion
Resistance spot and seam weld symbols are easiest to read when each element is handled in a fixed order: identify the governing standard, check symbol placement, read size, read length or pitch, confirm quantity, inspect the tail, and then check supplementary contour requirements.
The most important freshness correction is the AWS A2.4:2020 strength rule. For spot and seam welds, the left-side value now represents weld size—spot diameter or seam width—while a specified strength belongs in a tail note. Keeping that rule, side significance, pitch, quantity, and contour requirements separate helps prevent costly fabrication and inspection errors.
