At first glance, the appearance of weld symbols on an engineering blueprint or fabrication drawing may look like strange hieroglyphics. In reality, these symbols represent a simple language that is used to communicate important information to welders. This article examines common weld symbols and what they mean.

Welding Symbols Quick Card
  • Builder's Book Inc. (Author)
  • English (Publication Language)
  • 6 Pages - 02/14/2010 (Publication Date) - Builder's Book Inc. (Publisher)
Welding: Principles and Applications
  • Hardcover Book
  • Jeffus, Larry (Author)
  • English (Publication Language)

Weld Symbols

Fabrication and engineering drawings frequently feature a set of symbols that substitute for written instructions about how a weld should be completed. The symbol shown reflects the size of weld that should be used, the type of weld and any specific finishing or processing requirements. Even when a brief description is given on the fabrication drawing, it may not be entirely clear what is meant by the symbol. This article will look at some of the most frequently used weld symbols and exactly what they mean.


Weld symbols were developed to provide a consistent and uniform method of adding weld information to construction drawings and engineering plans. With a few lines, shapes and numbers, the simple symbols can convey the most important aspects of the weld, including location, type, and depth.

In the United States, the American Welding Society and American National Standards Institute work together to publish a standardized list of weld symbols to be used in all welding operations. Having a standardized list helps to ensure that welds are properly completed by the welder, no matter where that welder might be working. While not every detail may be present in the symbol, the weld basics are given. To an experienced welder, the basics will tell them everything they need to know to move forward with the fabrication plans.

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Anatomy of a Weld Symbol

It’s important to understand the backbone of every weld symbol. Each symbol starts with an anchor or a reference line. This horizontal line is the basis for each symbol and tells how the weld should be completed. Every other part of the symbol is connected to, and relates to, this baseline.

Typically, there are arrows pointing to a position on the line that is where the weld should be completed. In other cases, a circle or some other shape will be used to represent the weld point. Newer charts may designate the weld site by using a different color or shading as the indicator. A circle around a T-joint or Y-joint indicates that all three connection points should be welded.

Symbols for Weld Types

Even though there are many different weld operations, the basic instructions are very similar. There are three main types of welds designated by symbols: slot or plug welds, fillet welds and groove welds. Each weld type has its own unique features.

Slot and Plug Welds

Slot and plug weld symbols are used to designate welds where two pieces of material overlap each other. One of the pieces will have holes in it. These holes are usually long and narrow for spot welds and round for plug welds. During the weld, a bonding material is dropped into the hole and forms the basis for the completed weld.

On drawings, slot welds should have a number to the left of the symbol that designates the width of the slot. To the right of the symbol are numbers separated by a dash, representing the length and pitch of the slot. Arrows will frequently point to which piece of material should have the slot.

Plug weld symbols will list the diameter size of the hole on the left side of the symbol. Pitch or spacing requirements are then listed to the right of the symbol. Similar arrows as those used in slot weld symbols will designate which piece of material has the hole where the bonding material should be placed.

Fillet Welds

Fillet welds are used to create T joints, as well as corner and lap joints. The fillet symbol will show a triangular shape that specifies where the weld material should be placed and welded to complete the bond. Some joints allow for the welding material to be placed on either side of the joint, while others specify whether only one side or both sides should be used.

The size of the weld is written to the left of the symbol, no matter where the weld should be completed. Sometimes this size is on the right of the symbol, but usually, a number on the right side represents a second weld size for the mirror side of the joint.

Groove Welds

There are several types of groove welds, so these are the symbols you may see most often. Groove welds are often used to connect two materials that are placed next to each other. Additionally, some T joints and corner joints may also require this type of weld. Groove welds are differentiated by the edge shape of one or both material pieces to be joined. While fillet welds usually have square edges, groove welds generally join at least one edge that is not square. A groove weld is also necessary when two square-edged pieces require spacing between them in the finished weld.

Bevel Groove Weld

The bevel groove weld joins together a piece of material with a slanted or rounded edge with another piece that has a flat edge. There should be an arrow in the symbol pointing to the piece of material with the angled end. Numbers may be shown above the weld symbol that specifies the degree of angle on the beveled edge, as well as the depth of the weld.

J-Groove Welds

When one piece of material has a square edge and the edge of the adjoining piece is concave, a J-groove weld will be indicated. The depth of the groove opening and degree of separation will be listed as numbers near the symbol. If the weld penetration needs to be greater than the throat depth, another number will be listed in parentheses to indicate the penetration depth.

U-Groove Welds

In a case where both materials to be joined have concave ends, a U-groove weld will be warranted. Similar to the J groove, this symbol will display numbers showing the edge treatment depth and degree of opening when the pieces are placed next to each other. Numbers in parentheses will be present if the weld penetration needs to be deeper than the throat depth.

V-Groove Welds

Both material edges for a V-groove weld are slant or bevel, creating a V shape. Numbers along the weld symbol will list the degree of opening when they place the materials side by side. A double-V connection will have a measurement above the weld symbol to show the spacing that should be present between the material edges. They listed an additional measurement to indicate that the weld should penetrate deeper than the opening created by the V.

Flare-V Groove Welds

They use the Flare-V welds to join materials when both have rounded or curved ends. They also use this weld to join materials that are completely round. Arrows will designate the weld point, and numbers should specify the depth of the weld and any required penetration.

Square Groove Welds

They use the square groove weld to join materials with straight or perpendicular edges. One or two arrows may point to the weld site. Above the weld symbol, a number will detail the width of any spacing needed for the weld.

Flare Bevel Groove Welds

This weld symbol is used when around material is being attached to a flat material. Two numbers should be present with the symbol. The first number indicates the depth of the weld material. A second number shown in parentheses will indicate how deep the weld should penetrate.

Backing Bar Symbol

They added the backing bar symbol to groove-weld symbols to further clarify weld requirements. The square or rectangular addition to the symbol shows the need to include a support to the back of the weld joint for the joining process. If the letter R is present with the symbol, they remove the backing bar after the weld is complete.

Melt-Thru Symbol

Another clarifying symbol for groove welds is the melt-thru indication. They added it to the symbol as a half moon or three-quarter-circle shape. This marker is usually accompanied by a measurement to indicate the height of the reinforcement if that height is essential to the weld specification. They use this indicator when the weld completely penetrates, and the weld performs from only one side of the materials.

Finishing Symbols

Specific requirements may be necessary for the proper finishing of a weld joint. To keep communicating this requirement as simple as possible, they often added the procedure for finishing to the weld symbol by means of a letter designation placed above the weld symbol. Listed below are the most common finish symbols:

  • Chipping
  • G: Grinding
  • H: Hammering
  • M: Machining
  • P: Planishing
  • R: Rolling
  • U: Unspecified

Practical Application

The genius of this symbolling system is that it makes communication between the engineer or plan designer and the welder simple and consistent. With just a few lines, letters and numbers, a unique language allows the welder to review the plans and quickly get to work. Since the symbols are used nationwide, trained welders can work in any welding application. This simplicity of information transfer should encourage every welder to take the time to learn the basics of weld symbols and what they mean.

Featured image: CC0 Public Domain JonKline via Pixabay

Welding Symbols Quick Card
  • Builder's Book Inc. (Author)
  • English (Publication Language)
  • 6 Pages - 02/14/2010 (Publication Date) - Builder's Book Inc. (Publisher)
Welding: Principles and Applications
  • Hardcover Book
  • Jeffus, Larry (Author)
  • English (Publication Language)

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