Welding Symbols Chart
How to read a welding symbol in AWS A2.4 conventions: the reference line, arrow side and other side, the tail, each basic weld symbol, the supplementary symbols, and where size, length, pitch, root opening and groove angle are written.
- Reference line
- The horizontal line everything hangs on. Always drawn horizontal.
- Arrow
- Points at the joint. The side of the joint it touches is the arrow side; the far side is the other side.
- Arrow side vs other side
- A weld symbol below the line is arrow side, above the line is other side, on both sides means weld both.
- Tail
- Optional. Holds the process, the specification or WPS, or a note. Left off when there is nothing to say.
Basic weld symbols
Each symbol is drawn on the arrow side (below the reference line) unless it has no side significance. Back welds are shown opposite the groove weld they back.
| Symbol | Weld | What it is | Dimensions |
|---|---|---|---|
| FilletFillet | A triangular weld in the corner of a T, lap or corner joint. The most common weld on fabrication drawings; no joint preparation needed. | Leg size to the left (unequal legs as 1/4 x 3/8, with the drawing showing which leg is which); length and pitch to the right. | |
| Square grooveGroove | A butt joint with unprepared, square edges. Suits thin material where the arc can penetrate without a bevel. | Weld size (depth of fusion) to the left; root opening (the gap) between the two lines. | |
| V-grooveGroove | Both edges beveled to form a V. Standard for full-penetration butt welds in plate; a double-V has the symbol on both sides of the line. | Groove depth with weld size in parentheses to the left; root opening inside the V; included groove angle beyond the open end of the V. | |
| Bevel grooveGroove | One edge beveled, the other square. Common on T and corner joints. The arrow breaks toward the member that gets the bevel when it matters which one. | Groove depth and weld size to the left; root opening inside; bevel angle beyond the open end. | |
| U-grooveGroove | Both edges machined to a radiused U. Uses less filler than a V on thick sections but costs more to prepare. | Groove depth and weld size to the left; root opening inside; groove angle beyond the open end. | |
| J-grooveGroove | One edge machined to a J (a radiused bevel), the other square. The half-U counterpart of the bevel groove; the arrow breaks toward the J member. | Groove depth and weld size to the left; root opening inside; groove angle beyond the open end. | |
| Flare-V grooveGroove | The groove between two rounded surfaces, such as two tubes or bars side by side, or two formed radii. | Weld size to the left, with the depth of the flare groove when it matters; length and pitch to the right. | |
| Flare-bevel grooveGroove | The groove between a rounded surface and a flat one, such as a tube or formed edge against plate. | Weld size to the left; length and pitch to the right. | |
| Plug or slotPlug and slot | A weld that fills a round hole (plug) or an elongated hole (slot) in one member to join it to the member behind. The arrow side is the member with the hole. | Hole diameter (or slot width) to the left; depth of fill inside the symbol when not full; countersink angle beyond it; pitch to the right. Slot length and orientation are shown on the drawing or a detail. | |
| Spot or projectionSpot, projection and seam | Discrete welds between overlapping sheets, usually resistance welded. Centered on the line it has no arrow or other side; the process (for example RSW) goes in the tail. | Spot diameter or shear strength to the left; pitch to the right; number of welds in parentheses. | |
| SeamSpot, projection and seam | A continuous line of overlapping spot welds between sheets, made with roller electrodes (or by other processes). Used for leak-tight lap joints. | Seam width or strength to the left; length to the right. | |
| Back or backingBack and backing | A weld bead on the opposite side of a groove weld. A back weld goes in after the groove weld; a backing weld goes in first. Same symbol for both: a tail note or a multiple reference line tells you the order. | Always on the side of the line opposite the groove weld symbol. Height of reinforcement may be given to the left. | |
| SurfacingSurfacing | Weld metal laid on a surface rather than in a joint: hardfacing, buildup, cladding. Always drawn on the arrow side. | Minimum height of the deposit to the left; the extent of the area goes on the drawing. |
AWS A2.4 also defines scarf, stud and edge weld symbols, which are not drawn here. Summaries are ours; confirm against the A2.4 edition and the WPS your contract invokes.
Have a weldment to build? with certified welders.
Supplementary symbols
Weld all around
A circle where the arrow meets the reference line: the weld continues all the way around the joint, such as a tube to a plate.
Field weld
A small flag at the arrow and reference line junction: make this weld on site or at final assembly, not in the shop.
Melt-through
A filled half circle opposite a groove weld: full penetration from one side with visible root reinforcement on the back. The height of the root reinforcement may be given beside it.
Consumable insert
A square opposite a groove weld: a preplaced filler ring or insert at the root, fused into the weld. The insert class goes in the tail.
Backing
A rectangle opposite a groove weld: a backing bar or strip behind the root. An R inside means remove it after welding; the backing material and size are called out in the tail or on the drawing.
Spacer
A rectangle drawn through the reference line, breaking it: a spacer strip sits in the root of a double-sided groove weld. Its material and size are specified separately.
Contour: flush or flat
A straight line across the face of the weld symbol: finish the weld face flush or flat. A letter over it gives the method (C chip, G grind, H hammer, M machine, R roll, P planish, U unspecified).
Contour: convex
An arc bowing away from the weld symbol: the finished face must be convex (crowned). A finishing letter may go with it.
Contour: concave
An arc bowing toward the weld symbol: the finished face must be concave (dished). Most often seen on fillet welds for fatigue.
Where the numbers go
| Dimension | Where it goes | Example |
|---|---|---|
| Size | Left of the weld symbol, same side of the line | 1/4 fillet leg; groove depth S with weld size (E) in parentheses, e.g. 1/2 (3/8) |
| Length | Right of the weld symbol | 6 means a 6 in long weld; no length means the full joint |
| Pitch | Right of the length, after a hyphen | 2-6: 2 in welds on 6 in centers (intermittent) |
| Root opening | Inside the groove weld symbol | 1/8 gap between the members at the root |
| Groove angle | Beyond the open end of the groove symbol | 60° included angle for a V; the bevel angle for a bevel |
| Number of welds | In parentheses near a spot, projection or plug symbol | (6) for six spot welds |
| Contour and finish | Over the face of the weld symbol | Flush line with G: grind flush |
| Process and references | In the tail | GMAW, SMAW, a WPS number or a note |
Reading rules that catch people out
- The reference line is always drawn horizontal. The arrow can leave either end and bend at any angle; it points at the joint.
- Fillet, bevel, J and flare-bevel symbols always keep their perpendicular leg on the left, whichever way the arrow points.
- On bevel and J grooves the arrow is broken (jogged) toward the member that gets prepared, when it matters which one.
- Weld symbols on both sides of the line mean weld both sides. For intermittent welds, symbols lined up across the line mean chain; offset symbols mean staggered.
- Multiple reference lines show a sequence: the line nearest the arrow is the first operation, the next line out is the second.
- No length dimension means weld the full length of the joint, stopping at abrupt changes in direction unless the weld-all-around circle carries it around.
Frequently asked questions
- What does it mean when the weld symbol is below the reference line?
- Below the line means arrow side: make the weld on the side of the joint the arrow touches. Above the line means other side. Symbols on both sides mean weld both sides. This holds whichever way the arrow points or which end the tail is on.
- What is the difference between a weld symbol and a welding symbol?
- In AWS usage the weld symbol is just the shape that names the weld type, such as the fillet triangle. The welding symbol is the whole assembly: arrow, reference line, tail, weld symbol, dimensions and supplementary symbols.
- What does 1/4 with 2-6 mean on a fillet weld symbol?
- A 1/4 in leg fillet weld, made in 2 in long segments spaced 6 in center to center (intermittent). With the fillet on both sides and the segments lined up it is chain intermittent; with the segments offset it is staggered.
- What does the flag on a welding symbol mean?
- A field weld: the weld is made at the job site or at final installation rather than in the fabrication shop. It matters for quoting because field welding is priced and scheduled differently.
- Why do some welding symbols have no tail?
- The tail only appears when there is something to put in it: a welding process (GMAW, GTAW, SMAW), a WPS or specification number, or a note. With nothing to reference, it is left off.
- Are AWS and ISO welding symbols the same?
- The weld shapes are close, but the layout differs. ISO 2553 adds a dashed identification line next to the reference line to show which side is which, so the AWS rule of below-the-line means arrow side does not carry over. Read ISO drawings against ISO 2553.
