Fillet welds are everywhere in metal fabrication, used to join pieces at T-joints, lap joints, and corners.
The fillet weld symbol illustrates how to create these triangular welds, including size, length, and position. Reading these symbols correctly is essential; mistakes can result weak joints or failed inspections.
Fortunately, fillet weld symbols follow a logical, easy-to-learn system.
In this guide, you’ll discover how to read each part of the fillet weld symbol, understand placement rules, and follow global welding standards.
Soon, you’ll interpret these symbols confidently and use them in all your welding projects.
Quick Insights:
- A fillet weld symbol indicates a triangular weld between two surfaces.
- Symbols include weld size, length, contour, and finishing details.
- Arrow side vs. other side placement affects weld positioning.
- Common supplementary symbols specify grinding, chipping, or post-weld treatments.
What Is a Fillet Weld Symbol?
A fillet weld symbol is a standardized drawing symbol that tells welders exactly how to join two metal pieces at an angle. The symbol utilizes a triangular shape, along with reference lines and arrows, to indicate the weld location, size, and requirements.
Definition and Purpose
A fillet weld symbol communicates the exact requirements for creating a triangular-shaped weld between two surfaces. The symbol appears on engineering drawings and blueprints to guide welders.
The primary purpose is to provide clear, standardized instructions. You can understand the weld size, location, and technique just by reading the symbol. This prevents mistakes and ensures consistent results across different projects.
Fillet weld symbols work with three main joint types:
- T-joints, where pieces meet at right angles
- Lap joints where pieces overlap
- Corner joints where pieces form a corner
The symbol eliminates guesswork. Instead of written instructions, you get a visual guide that shows exactly what the finished weld should look like.
Visual Representation on Drawings
The fillet weld symbol looks like a right triangle on technical drawings. You will see this triangle positioned either above or below a horizontal reference line.
An arrow extends from the reference line and points to the actual joint location on the part. The triangle's position tells you which side of the joint to weld.
When the triangle is positioned below the reference line, weld on the arrow side. When it sits above the line, you weld on the opposite side of where the arrow points.
Numbers often appear next to the triangle. These numbers show the leg size of the weld in inches or millimeters.
For example, a "1/4" means each leg of the triangular weld should measure 1/4 inch.
Key Components of the Symbol
To understand fillet weld symbols, you first need to know the main parts of a fillet weld and how to measure them.
- Root: This is where the two plates meet at the bottom of the joint. The root of the weld is where the weld metal reaches past this point.
- Leg: The leg is how we measure the size of a fillet weld. It’s the distance from the flat plate to the weld’s outer edge, called the toe. You can use a fillet gauge to measure the leg.
- Face: The face is the visible surface of the weld. It can look curved out (convex), curved in (concave), or flat.
- Toe: The toe is the edge of the weld. Problems like undercut often happen here.
- Throat: There are two throat types. The theoretical throat runs from an imaginary line between the toes down to the root. The actual throat is the distance from the root to the weld’s face.
Anatomy of a Fillet Weld Symbol
A fillet weld symbol has four main parts that work together to show welders exactly what to do. The reference line acts as the base, while the arrow side and other side tell you where to place the weld, and the triangle symbol identifies it as a fillet weld.
Reference Line
The reference line is always drawn as a straight horizontal line. This line serves as the foundation for all welding symbol information.
You will see the reference line in the center of every welding symbol. It connects the arrow line on one end and the tail on the other end.
The reference line has two sides that matter:
- Below the line - This is the arrow side
- Above the line - This is the other side
All weld symbols attach to this reference line. The position of symbols on the line tells you important details about where to make the weld.
Arrow Side and Other Side
The arrow side and the other side of the system tell you exactly where to place your weld. This system prevents confusion about weld location.
When you see a fillet weld symbol below the reference line, you make the weld on the arrow side. The arrow side is the joint side toward which the arrow line points.
If the fillet weld symbol appears above the reference line, you weld on the other side. The other side is opposite to where the arrow points.
Sometimes you will see fillet weld symbols on both sides of the reference line. This means you need to make fillet welds on both sides of the joint.
The arrow line always points to the specific joint where welding will happen. This arrow line connects to the reference line and shows you the exact location.
The Triangle Symbol
The triangle symbol identifies a fillet weld on drawings. This symbol looks like a right triangle with the right angle at the reference line.
You will always see this triangle touching the reference line. The triangle can appear above or below the line, depending on the location of the weld.
Numbers next to the triangle show the weld size. These numbers tell you the leg length of the fillet weld in inches or millimeters.
The triangle symbol is standard worldwide. All welders recognize this symbol as meaning fillet weld, regardless of country or company.
Weld Location
The weld location depends on which side of the reference line the triangle symbol is located. This system ensures accurate weld placement every time.
Arrow-side welds occur when the triangle appears below the reference line. You make these welds on the same side as the arrow points.
Other side welds occur when the triangle sits above the reference line. These welds are located on the opposite side of the arrow direction.
Both sides welding requires triangle symbols above and below the reference line. You must complete fillet welds on both sides of the joint in these cases.
How to Read Fillet Weld Symbols
Reading fillet weld symbols requires understanding three main parts: the position of the triangle symbol relative to the reference line, the numbers indicating leg size measurements, and the additional notations specifying weld length and spacing.
Arrow Side versus Other Side Interpretation
The triangle symbol's position tells you exactly where to place the fillet weld. When the triangle is positioned below the reference line, weld on the arrow side. When the triangle appears above the reference line, you weld on the other side.
The arrow side refers to the joint side toward which the arrow points. The other side is the opposite side of the joint from where the arrow points.
You can have triangles on both sides of the reference line. This means you need fillet welds on both sides of the joint. Each triangle can have different size requirements.
The reference line runs horizontally through the welding symbol. The arrow connects to this line and points to the specific joint location on your workpiece.
Leg Size and Notation
The leg size appears as a number to the left of the triangle symbol. This number tells you the weld size in inches or millimeters. For example, a "1/4" means that each leg of the fillet weld should be 1/4 inch thick.
Fillet welds have two legs that form the triangular cross-section. Most of the time, both legs are the same size. When you see one number, both legs use that measurement.
Sometimes you need different leg sizes. The symbol shows this as two numbers separated by an "x". The first number is the vertical leg, and the second number is the horizontal leg.
No number on the symbol indicates that the leg size is determined in the field or by other specifications. Always check your drawing notes for additional size information.
Length and Pitch Designation
The weld length appears to the right of the triangle symbol. This number indicates the duration of each weld. A "3" means each fillet weld section is 3 inches long.
Pitch designation shows the spacing between intermittent welds. You'll see this written as length-pitch, like "3-6". This means 3-inch welds with 6-inch spacing between the start of each weld.
When you don't see a length number, the fillet weld runs continuously along the entire joint. This is common for structural connections that need full strength.
Multiple weld segments use the same length and pitch unless the symbol shows different numbers. The pitch measurement includes the weld length plus the gap to the next weld start.
Fillet Weld Symbol Placement and Joints
Fillet weld symbols are placed on welding drawings to show where welds go on three main joint types. The symbol placement indicates which side of the joint will be welded and how the parts connect.
Lap Joint Applications
A lap joint forms when two metal pieces overlap each other. The fillet weld symbol is placed on the reference line to indicate where you weld the overlapping edges.
Place the symbol below the reference line for arrow-side welding. This means you weld on the side where the arrow points. The symbol above the reference line indicates other-side welding.
Key placement rules for lap joints:
- Arrow side: Symbol below reference line
- Other side: Symbol above reference line
- Both sides: Symbols above and below the reference line
The triangular fillet weld symbol shows the approximate shape of the finished weld. Your weld should fill the corner where the two overlapping pieces meet.
Corner Joint Applications
Corner joints happen when two pieces of metal meet at their edges to form a corner. The fillet weld symbol placement works the same way as other joints.
You can weld corner joints on the inside, outside, or both sides of the corner. The symbol position on the reference line tells you exactly where to place your weld.
Inside corner welds use symbols placed according to the direction of the arrow. Outside corner welds follow the same symbol rules but go on the opposite surface.
Most corner joint fillet welds create a 90-degree angle between the metal pieces. Your finished weld should have a triangular cross-section that fills the corner space completely.
T-Joint and Other Common Configurations
T-joints form when one piece of metal connects perpendicular to another piece. This creates a T-shape that needs fillet welds on one or both sides.
The vertical piece in a T-joint can be welded to the horizontal piece on either side. Symbol placement below the reference line means arrow side welding. Symbol placement above means other side welding.
Common T-joint welding patterns:
- Single side: One fillet weld symbol
- Double side: Symbols above and below reference line
- Intermittent: Symbols with length and spacing dimensions
Your fillet welds on T-joints should connect the vertical piece firmly to the horizontal base. The weld metal fills the 90-degree angle between both pieces.
Standards and Reference Charts for Fillet Weld Symbols
Several standards govern fillet weld symbols, with the American Welding Society (AWS) being the primary authority in North America. These standards provide detailed charts and reference materials that help welders accurately interpret symbols.
American Welding Society Standards
AWS creates the official rules for welding symbols in North America. Their main document is AWS A2.4, which covers all welding symbols, including fillet welds.
This standard defines a fillet weld as "a weld of approximately triangular cross-section joining two surfaces approximately at right angles to each other." AWS also publishes AWS A3.0, which gives you the exact definitions of welding terms.
You need to follow these standards because they ensure everyone uses the same symbols. This prevents mistakes and makes drawings clear for all welders and engineers.
AWS updates these standards regularly. New versions include changes in technology and industry practices.
Weld Symbols Chart
A weld symbols chart shows you what each symbol means. These charts display the basic fillet weld symbol as a right triangle placed on the reference line.
The chart shows important details like:
- Symbol placement above or below the reference line
- Size dimensions and where they go
- Length specifications
- Spacing requirements
- Finishing symbols
Most welding shops have these charts posted on walls. You can also find them in welding handbooks and online resources.
The charts use visual examples to show how symbols look on actual drawings. This helps you learn faster than reading text descriptions alone.
ISO Versus AWS Notation
ISO standards differ from AWS standards in several ways. The International Organization for Standardization uses different symbols and placement rules.
AWS places the fillet symbol as a triangle on the reference line. ISO employs a different approach, utilizing alternative symbol shapes and positions.
You need to know which standard your drawings follow. Most North American projects use AWS notation. European and international projects often use ISO standards.
The size dimensions also work differently between systems. AWS displays leg size, while ISO may display throat thickness or other measurements.
Also Read: Welding Weave Patterns
Differences from Groove and Square Groove Welds
Fillet welds use different symbols and placement rules compared to groove welds. Field welding marks and multiple weld indicators follow specific patterns that help welders understand exactly what work needs to be done.
Field Weld and All Around Symbols
The field weld symbol looks like a small flag or pennant. You place this symbol at the junction where the reference line meets the arrow.
When you see this flag symbol, it means the welding happens on site. The weld is not done in the shop or factory.
Key points about field weld symbols:
Always appears at the arrow and reference line junction
- Indicates on-site welding work
- Used with any type of weld symbol
- Shows up on both partial and complete joint welds
The all-around symbol is a small circle. It goes at the same junction point as the field weld flag.
This circle indicates that you should weld completely around the joint. You make a continuous weld that encircles the entire connection.
Multiple Welds and Both Side Indications
You can show welds on both sides of a joint using the reference line. Put one symbol above the line and another below it.
The symbol above the reference line means the arrow side. The symbol below the line means the other side.
Both side weld indicators
- Arrow side symbol goes above the reference line
- Other side symbol goes below the reference line
- Both symbols can be the same or different types
- Size numbers go next to each symbol
For multiple fillet welds, you repeat the triangle symbols. Each triangle shows a separate weld location.
You can also use numbers to indicate the number of welds required. Write the number in parentheses near the symbol.
Differences from Groove and Square Groove Welds
Fillet welds use a triangle symbol that sits on the reference line. Groove welds use different shapes that represent the joint preparation.
Square groove welds are represented by a rectangle or square symbol. V-groove welds look like a V shape.
Main differences:
- Fillet welds join surfaces at angles, usually 90 degrees
- Groove welds join materials end to end or edge to edge
- Square groove welds have no joint preparation or beveling
- Fillet weld symbols always use the triangle shape
The size measurement also works differently. Fillet welds measure the leg length of the triangle. Groove welds measure the depth of penetration or throat thickness.
Fillet welds don't need root openings or backing symbols. These features only apply to groove type welds.
Final Thoughts
Mastering fillet weld symbols gives you precision in fabrication and helps you avoid costly quality issues. When you understand these symbols correctly, your welds consistently meet design requirements.
The triangular symbol may look simple, but it carries important information. Size, length, and position details all matter for strong joints.
Practice reading symbols regularly to build your skills. Begin with basic fillet welds before progressing to more complex joints.
When you have doubts about symbol interpretation, always reference these standards:
- ANSI/AWS A2.4 - Standard Symbols for Welding, Brazing, and Nondestructive Examination
- ISO 2553 - Welding and Allied Processes
These documents provide official guidance for symbol meanings. They help you avoid mistakes that could weaken your welds.
Remember these key points:
- Arrow side versus other side placement
- Weld size measurements
- Length and spacing requirements
- Contour symbols when specified
Your welding career benefits when you read symbols accurately. Employers value welders who can understand drawings without needing constant clarification.
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Frequently Asked Questions
The fillet weld symbol appears as a triangle on welding drawings. You can specify these welds using size numbers, length measurements, and special symbols for finishing requirements.
What does the fillet weld symbol look like?
The fillet weld symbol looks like a right triangle. The triangle sits either above or below the reference line on welding drawings.
When the triangle appears below the reference line, it means weld the arrow side. When it appears above the reference line, you weld the other side.
The triangle shape matches the cross-section of the actual weld. This makes it easy to remember what the symbol represents.
How do you specify a fillet weld?
You specify a fillet weld by placing a number to the left of the triangle symbol. This number shows the leg size of the weld in fractions of an inch or millimeters.
The weld length goes to the right of the triangle symbol. If you see no length specified, you weld the entire joint length.
Pitch spacing appears after the length measurement. This tells you how far apart to space intermittent welds.
What is a 6 fillet weld?
A 6 fillet weld means the weld has 6-millimeter legs. In metric drawings, the number refers to millimeters.
Both legs of the triangle-shaped weld measure 6mm from the root to the face. This creates a specific throat thickness that determines the weld's strength.
You might also see 1/4 inch fillet welds in imperial drawings. The measurement system depends on your drawing standards.
What does a finish contour symbol on a fillet weld mean?
A finish contour symbol shows how to shape the weld face after welding. You'll see these as curved or straight lines added to the basic triangle symbol.
A curved line means you need a convex or concave weld face. A straight line means you need a flat weld face.
The symbol also tells you the finishing method. Common methods include grinding, machining, or hammering to achieve the required shape.
Can a fillet weld have different leg sizes?
Yes, fillet welds can have unequal leg sizes. You show this by placing two numbers separated by an "x" to the left of the triangle symbol.
The first number represents the vertical leg size. The second number represents the horizontal leg size.
For example, "6x8" means a 6mm vertical leg and an 8mm horizontal leg. This creates an unequal leg fillet weld for specific joint requirements.