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Weld symbol chart

A welding symbol is a horizontal reference line with an arrow pointing at the joint: a weld symbol below the line calls for the weld on the arrow side, one above it for the other side, with the weld's size to the left of the symbol, its length and pitch to the right, and a process or specification in the tail at the far end. The weld symbol chart draws and explains each part of the AWS A2.4 welding symbol - the weld and groove weld symbols, supplementary symbols such as weld all around and field weld, the dimensions, and the finishing and process letters - and its reader explains a welding symbol written in words, part by part and aloud.

59 elements, by group.

Parts of the welding symbol

The reference line, the arrow and the tail, and how the side of the line a weld symbol sits on says which side of the joint is welded.

Reference line
Part of the symbol
Where it sits: The horizontal line every welding symbol is built on; the arrow joins one end of it.
It carries everything else: a weld symbol below it describes the weld on the arrow side, above it the other side, with the dimensions beside the weld symbol.
Arrow
Part of the symbol · also called leader
Where it sits: From one end of the reference line to the joint; it may leave either end.
It points at the joint to be welded, and the side of the joint it touches is the arrow side.
Tail
Part of the symbol
Where it sits: The fork at the end of the reference line away from the arrow.
It holds a reference the symbol does not otherwise show - a specification, a process or another reference - and is left off when there is none.
Arrow side
Part of the symbol · also called below the line
Where it sits: Below the reference line.
A weld symbol below the line calls for the weld on the side of the joint the arrow points to.
ISO 2553 draws a dashed identification line beside the continuous reference line; a symbol on the continuous line is on the arrow side.
Other side
Part of the symbol · also called above the line
Where it sits: Above the reference line.
A weld symbol above the line calls for the weld on the side of the joint opposite the arrow.
In ISO 2553 a symbol on the dashed identification line is on the other side.
Both sides
Part of the symbol · also called double
Where it sits: Above and below the reference line.
Weld symbols on both sides of the line call for a weld on each side of the joint, such as a fillet on each side of a T-joint.
ISO 2553 leaves the dashed identification line out for a weld symmetrical about the joint.
No arrow-side or other-side significance
Part of the symbol · also called centered on the line
Where it sits: Centered on the reference line.
A spot, projection, seam or square-groove symbol drawn across the line belongs to neither side.
Broken arrow
Part of the symbol · also called bent arrow
Where it sits: The arrow, bent partway, on a bevel, J or flare-bevel weld symbol.
Where only one member of the joint is prepared, the break points the arrow at the member that is.
Multiple reference lines
Part of the symbol · also called sequence of operations
Where it sits: Two or more reference lines stacked on one arrow.
They give operations in order: the line nearest the arrow is the first, the next line the second.

Weld symbols

The shape on the reference line that names the kind of weld: below the line for the arrow side, above it for the other side.

Fillet weld
Weld symbol
Where it sits: A right triangle on the reference line, its upright leg always on the left.
A weld of roughly triangular cross-section joining two surfaces at about a right angle, as in a T-joint, lap joint or corner joint.
ISO 2553 gives a fillet weld's size with a letter: a for the throat thickness, z for the leg length.
Plug or slot weld
Weld symbol · also called plug weld, slot weld
Where it sits: A rectangle on the reference line, on the arrow side or the other side, never both.
A weld filling a round hole (plug) or an elongated slot (slot) in one member, joining it to the member behind.
Spot or projection weld
Weld symbol · also called spot weld, projection weld
Where it sits: A circle below or above the reference line, or centered on it when the side does not matter.
A weld at a small spot between overlapping members; a projection weld, made at projections formed on one member, shares the symbol.
Stud weld
Weld symbol
Where it sits: A circle with an X in it, below the reference line: arrow side only.
A stud, such as a threaded pin, is welded by its end to the surface the arrow points to.
Seam weld
Weld symbol · also called seam weld
Where it sits: A circle crossed by two lines parallel to the reference line, on one side or centered on it.
A continuous weld made between or over overlapping members, as one run or a row of overlapping spots.
Back or backing weld
Weld symbol · also called back weld, backing weld
Where it sits: An outlined half circle on the side of the line opposite a groove weld symbol.
A weld on the back of a groove weld: a back weld is made after the groove weld, a backing weld before it, and the drawing says which.
Surfacing weld
Weld symbol · also called surfacing, overlay, buildup
Where it sits: Two half circles below the reference line: arrow side only.
Weld metal built up on a surface, rather than joining parts, to restore a dimension or add a layer that resists wear or corrosion.
Edge weld
Weld symbol · also called edge joint
Where it sits: A rectangle divided down the middle, on the arrow side, the other side or both.
A weld along the edges of two or more members lying side by side, as in an edge joint of flanged sheet.

Groove weld symbols

The shape of the groove prepared between the members for a groove weld. A perpendicular leg is always drawn on the left.

Square-groove weld
Groove weld symbol · also called square butt, square groove
Where it sits: Two short parallel lines on the reference line, or across it.
A groove weld between square, unprepared edges, butted together or set with a gap.
V-groove weld
Groove weld symbol · also called V weld, double-V, vee
Where it sits: A V with its point on the reference line.
Both members are beveled into a V-shaped groove filled with weld; on both sides of the line it is a double-V.
Bevel-groove weld
Groove weld symbol · also called bevel, single bevel, double bevel
Where it sits: An upright line with a slanted line from its foot, the upright on the left.
Only one member is beveled, and the broken arrow points to it; on both sides of the line it is a double bevel.
U-groove weld
Groove weld symbol · also called U weld, double-U
Where it sits: A cup on a short stem, opening away from the reference line.
Both members are prepared with a round-bottomed groove, U-shaped across the joint.
J-groove weld
Groove weld symbol · also called J weld, double-J
Where it sits: An upright line with a curve from it, the upright on the left.
Only one member is prepared, with a round-bottomed groove shaped like a J, and the broken arrow points to it.
Flare-V-groove weld
Groove weld symbol · also called flare V
Where it sits: Two curves on the reference line, bowed toward each other.
A weld in the groove between two rounded members, such as two bars or two bent edges lying side by side.
Flare-bevel-groove weld
Groove weld symbol · also called flare bevel
Where it sits: An upright line and a curve bowed toward it, the upright on the left.
A weld in the groove between a rounded member and a flat one, such as a bar or tube against a plate.
Scarf joint (brazed)
Groove weld symbol · also called scarf, brazing
Where it sits: Two parallel slanted lines on the reference line.
AWS A2.4's symbol for a brazed scarf joint, in which the members' ends are cut at matching angles and overlapped.

Supplementary symbols

Marks added to a welding symbol: all around, in the field, melt-through, an insert, backing or a spacer, and the shape of the finished weld.

Weld all around
Supplementary symbol · also called all around
Where it sits: A circle where the arrow meets the reference line.
The weld continues all the way around the joint, as around a tube or the outline of a part.
Field weld
Supplementary symbol · also called site weld
Where it sits: A filled flag where the arrow meets the reference line.
The weld is made in the field, where the work is installed, rather than in the shop.
Melt-through
Supplementary symbol · also called melt-thru
Where it sits: A filled half circle on the side of the line opposite the weld symbol.
The weld, made from one side, must penetrate the joint completely, with its root reinforcement showing on the far side.
Consumable insert
Supplementary symbol · also called insert
Where it sits: A square on the side of the line opposite the groove weld symbol.
A filler metal insert is placed at the root of the joint before welding and melts into the weld.
Backing
Supplementary symbol · also called backing strip, backing bar
Where it sits: A rectangle on the side of the line opposite the groove weld symbol.
A strip or bar is placed against the root of the joint to support the molten weld metal.
Spacer
Supplementary symbol
Where it sits: A rectangle drawn across the reference line, in the groove weld symbol.
A strip is set between the members at the root of the groove, holding the gap while the joint is welded.
Flush or flat contour
Supplementary symbol · also called flush, flat
Where it sits: A straight line parallel to the reference line, just beyond the weld symbol.
The face of the weld is finished flush with the surface, or flat.
Convex contour
Supplementary symbol · also called convex
Where it sits: An arc bowing away from the weld symbol, just beyond it.
The face of the weld is finished convex, bulging outward.
Concave contour
Supplementary symbol · also called concave
Where it sits: An arc bowing toward the weld symbol, just beyond it.
The face of the weld is finished concave, dished inward.

Dimensions

Where the numbers go: the size to the left of the weld symbol, the length and pitch to its right, a groove's opening and angle beside it.

Weld size
Dimension · also called leg, size
Where it sits: To the left of the weld symbol, on its side of the line.
For a fillet, the leg size, as 1/4, and two sizes, as 1/4 x 3/8, for unequal legs; for other welds, the size or strength the drawing asks for, in the drawing's units.
ISO 2553 prefixes a fillet weld's size: a5 is a 5 mm throat, z7 a 7 mm leg.
Length
Dimension
Where it sits: To the right of the weld symbol.
A number alone to the right is the length of the weld; with none, the weld runs the full length of the joint.
Length and pitch
Dimension · also called intermittent weld, stitch weld, L-P
Where it sits: To the right of the weld symbol, joined by a hyphen, as 2-5.
An intermittent weld: segments of the first length, spaced center to center by the second, the pitch.
Depth of preparation and groove weld size
Dimension · also called S(E), depth of bevel, effective throat
Where it sits: To the left of a groove weld symbol, the groove weld size in parentheses, as 3/8 (1/2).
The first number is how deep the groove is prepared; the one in parentheses is the groove weld size, the depth the weld penetrates the joint.
Root opening
Dimension · also called gap, R
Where it sits: Inside the groove weld symbol, nearest the reference line.
The gap between the members at the root of the joint; for a plug or slot weld, the same place gives the depth of filling.
Groove angle
Dimension · also called included angle, A
Where it sits: Beyond the root opening, just outside the groove weld symbol.
The groove's included angle, as 60°; for a plug weld, the same place gives the included angle of the countersink.

Finishing letters

A letter beyond the contour symbol saying how the weld is brought to that contour: the method of finishing, not the degree of finish.

C, chipping
Finishing letter · also called chipped
Where it sits: Beyond the contour symbol: the mark furthest from the reference line.
The weld is chipped to the contour shown.
G, grinding
Finishing letter · also called ground
Where it sits: Beyond the contour symbol: the mark furthest from the reference line.
The weld is ground to the contour shown.
H, hammering
Finishing letter · also called hammered
Where it sits: Beyond the contour symbol: the mark furthest from the reference line.
The weld is hammered to the contour shown.
M, machining
Finishing letter · also called machined
Where it sits: Beyond the contour symbol: the mark furthest from the reference line.
The weld is machined to the contour shown.
R, rolling
Finishing letter · also called rolled
Where it sits: Beyond the contour symbol: the mark furthest from the reference line.
The weld is rolled to the contour shown.
U, unspecified
Finishing letter · also called any method
Where it sits: Beyond the contour symbol: the mark furthest from the reference line.
The weld is brought to the contour shown by a method the drawing leaves to the maker.

Process letters

Letters in the tail naming the welding process, as AWS A3.0 abbreviates it.

SMAW, shielded metal arc welding
Process letters · also called stick welding
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
An arc between a flux-covered electrode and the work; the covering shields the weld.
GMAW, gas metal arc welding
Process letters · also called MIG, MAG
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
An arc between a continuously fed wire electrode and the work, shielded by a gas supplied from outside.
GTAW, gas tungsten arc welding
Process letters · also called TIG
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
An arc between a tungsten electrode that does not melt and the work, shielded by gas, with filler metal added separately or not at all.
FCAW, flux cored arc welding
Process letters · also called flux core, flux-cored
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
An arc between a continuously fed tubular electrode, with flux in its core, and the work, with or without a shielding gas.
SAW, submerged arc welding
Process letters · also called sub arc
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
An arc between a bare wire electrode and the work, buried under a blanket of granular flux.
PAW, plasma arc welding
Process letters · also called plasma
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
An arc from a tungsten electrode, constricted by a nozzle into a narrow plasma jet, melts the joint.
OFW, oxyfuel gas welding
Process letters · also called gas welding
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
A flame of a fuel gas burned with oxygen melts the work, with or without filler metal.
OAW, oxyacetylene welding
Process letters · also called gas welding, torch welding
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
Oxyfuel gas welding with acetylene as the fuel gas.
ESW, electroslag welding
Process letters
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
The heat of current through a pool of molten slag melts the filler metal and the edges of the joint, usually thick plate welded vertically in a single pass.
EBW, electron beam welding
Process letters · also called e-beam
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
A focused beam of high-speed electrons melts the joint, usually in a vacuum.
LBW, laser beam welding
Process letters · also called laser welding
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
A focused laser beam melts the joint.
RSW, resistance spot welding
Process letters · also called spot welding
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
Overlapping members, clamped between electrodes, are joined at a spot by the heat of current flowing through them.
RSEW, resistance seam welding
Process letters · also called seam welding
Where it sits: In the tail, the fork at the end of the reference line away from the arrow.
Resistance welding between wheel electrodes, making a continuous seam or a row of overlapping spots.

The reference line and the arrow. It points at the joint to be welded, and the side of the joint it touches is the arrow side. The weld symbol sits on the line: here a V-groove, above the line, so on the other side.
T, the tail. It holds a reference the symbol does not otherwise show - a specification, a process or another reference - and is left off when there is none.
S(E), left of the weld symbol. S is the depth of the groove's preparation, or the size or strength of other welds; (E) is the groove weld size.
R, inside the weld symbol. The gap between the members at the root of the joint; for a plug or slot weld, the same place gives the depth of filling.
A, beyond it. The groove's included angle, as 60°; for a plug weld, the same place gives the included angle of the countersink.
The bar, then F. The contour symbol - flush, convex or concave - and beyond it the finishing letter: C, G, H, M, R or U.
L-P, right of the weld symbol. The length of the weld, or of each segment, and the pitch: the spacing of the segments, center to center.
(N). The number of spot, seam, stud, plug, slot or projection welds.
The circle and the flag. Where the arrow leaves the line: weld all around, and a field weld.

The figure draws a weld on the other side. On the arrow side every mark is the same, mirrored below the line, and with weld symbols on both sides each carries its own. The marks keep these places when the arrow is drawn from the line's other end, and the weld symbols stay within the line's length.

Weld symbol or welding symbol?

In AWS A2.4 the weld symbol is the small shape that names the kind of weld, such as the triangle of a fillet or the V of a V-groove. The welding symbol is the whole: the reference line, the arrow, the weld symbol, its dimensions, the supplementary symbols and the tail.

AWS A2.4 and ISO 2553

ISO 2553 is the international counterpart. The difference you will see first is the side: ISO draws a dashed identification line beside the continuous reference line, and a weld symbol on the continuous line is on the arrow side, one on the dashed line on the other side; a weld symmetrical about the joint has no dashed line. ISO also writes a fillet weld's size with a letter in front: a for the throat thickness, z for the leg length, so a5 is a 5 mm throat.

Sources: AWS A2.4, Standard Symbols for Welding, Brazing, and Nondestructive Examination (the symbols and their places checked against the chart AWS published for its 1998 edition); AWS A3.0, Standard Welding Terms and Definitions (the process letters); ISO 2553 where the international standard differs. Left out for want of certainty: the planishing letter some charts add to the finishing letters, how a backing to be removed is marked, the brazing and stud welding process letters, and the nondestructive examination symbols A2.4 also covers.

Fillet weld

The welding symbol Fillet · Arrow side · 1/4 · 6-12 · Field weld

Read aloud: A fillet weld with 1/4 legs, on the arrow side of the joint, in segments 6 long at a pitch of 12, center to center, made in the field rather than the shop.

Fillet Weld symbol: Fillet weld: A weld of roughly triangular cross-section joining two surfaces at about a right angle, as in a T-joint, lap joint or corner joint.
Arrow side Side: Below the reference line. A weld symbol below the line calls for the weld on the side of the joint the arrow points to.
1/4 Size: Legs of 1/4, in the drawing's units.
6-12 Length and pitch: An intermittent weld: segments 6 long, spaced 12 apart center to center.
Field weld Supplementary symbol: The weld is made in the field, where the work is installed, rather than in the shop.

How do you read a welding symbol?

Start at the reference line, the horizontal line the arrow joins. The weld symbol on it names the kind of weld, and its side says where: below the line on the arrow side of the joint, above it on the other side, on both for both. The weld's size is to the left of the weld symbol and its length, or length and pitch, to the right; a groove's root opening, groove angle, contour and finishing letter stack outward from the line. A circle where the arrow meets the line means weld all around, a flag means a field weld, and the tail at the far end holds the process or specification.

What is the difference between the arrow side and the other side?

The arrow side is the side of the joint the arrow touches, and a weld symbol below the reference line is welded there. The other side is the side opposite, shown by a weld symbol above the line. Weld symbols on both sides of the line call for a weld on each side of the joint, such as a fillet on each side of a T-joint.

What does the triangle on a weld symbol mean?

A fillet weld. A weld of roughly triangular cross-section joining two surfaces at about a right angle, as in a T-joint, lap joint or corner joint. The triangle's upright leg is always drawn on the left, the number to its left is the leg size, and a number to its right is the length.

What does the flag on a welding symbol mean?

A field weld. The weld is made in the field, where the work is installed, rather than in the shop. The flag sits where the arrow meets the reference line.

What does a circle on a welding symbol mean?

It depends on where it is. A circle where the arrow meets the reference line means weld all around: the weld continues all the way around the joint, as around a tube or the outline of a part. A circle on the line itself is a spot or projection weld; with an X in it, a stud weld; crossed by two lines, a seam weld.

What do the numbers on a fillet weld symbol mean?

The number to the left of the triangle is the leg size, as 1/4. The number to the right is the length; two numbers joined by a hyphen, as 2-5, mean an intermittent weld of 2-long segments spaced 5 apart center to center. With no length, the weld runs the full length of the joint.

What is the difference between a weld symbol and a welding symbol?

How do ISO weld symbols differ from AWS?

ISO 2553 draws a dashed identification line beside the continuous reference line; a symbol on the continuous line is on the arrow side. In ISO 2553 a symbol on the dashed identification line is on the other side. ISO 2553 gives a fillet weld's size with a letter: a for the throat thickness, z for the leg length.

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Parts of the welding symbol

Reference line

Arrow

Tail

Arrow side

Other side

Both sides

No arrow-side or other-side significance

Broken arrow

Multiple reference lines

Weld symbols

Fillet weld

Plug or slot weld

Spot or projection weld

Stud weld

Seam weld

Back or backing weld

Surfacing weld

Edge weld

Groove weld symbols

Square-groove weld

V-groove weld

Bevel-groove weld

U-groove weld

J-groove weld

Flare-V-groove weld

Flare-bevel-groove weld

Scarf joint (brazed)

Supplementary symbols

Weld all around

Field weld

Melt-through

Consumable insert

Backing

Spacer

Flush or flat contour

Convex contour

Concave contour

Dimensions

Weld size

Length

Length and pitch

Depth of preparation and groove weld size

Root opening

Groove angle

Finishing letters

C, chipping

G, grinding

H, hammering

M, machining

R, rolling

U, unspecified

Process letters

SMAW, shielded metal arc welding

GMAW, gas metal arc welding

GTAW, gas tungsten arc welding

FCAW, flux cored arc welding

SAW, submerged arc welding

PAW, plasma arc welding

OFW, oxyfuel gas welding

OAW, oxyacetylene welding

ESW, electroslag welding

EBW, electron beam welding

LBW, laser beam welding

RSW, resistance spot welding

RSEW, resistance seam welding