AWS A2.4 weld symbol
Fillet Weld Symbol
A fillet weld symbol is a right triangle on the reference line, and it calls for a triangular weld in the corner of a lap or T-joint — the most common weld symbol on any drawing.
How to read the fillet weld symbol
- The perpendicular leg of the triangle is always drawn on the left, regardless of which side of the reference line the symbol sits on.
- A triangle below the reference line means weld the arrow side; above means the other side; both means fillets on both sides of the joint.
- The leg size goes to the left of the triangle. A single number means both legs are equal; two numbers in parentheses give unequal legs.
- The weld length goes to the right of the triangle.
- Length and pitch separated by a dash, such as 2-5, means 2 in long welds on 5 in centres — an intermittent fillet.
Where the dimensions go
| Position | What it specifies |
|---|---|
| Left of the symbol | Leg size, for example 1/4 |
| Right of the symbol | Length of weld, and pitch if intermittent, for example 3-6 |
| In the tail | Process or specification reference, for example GMAW |
Joint types
- T-joint
- Lap joint
- Corner joint
Practical notes
- Fillet welds need no joint preparation, which is why they are the cheapest weld to specify.
- The theoretical throat of an equal-leg fillet is the leg size multiplied by 0.707 — that is the dimension the joint's strength actually depends on.
- Staggered intermittent fillets are shown by offsetting the symbols above and below the reference line.
Fillet Weld symbol — common questions
What does the fillet weld symbol look like?
A right triangle sitting on the reference line, with the perpendicular leg drawn on the left side. Below the reference line means weld the arrow side; above means the other side.
Which side of the reference line means arrow side?
Below. A weld symbol drawn below the reference line calls for a weld on the side of the joint the arrow touches. Above the line means the opposite side.
What does 1/4 to the left of a fillet symbol mean?
A 1/4 inch leg size on both legs of the fillet. Two numbers in parentheses indicate unequal legs, with the drawing showing which leg is which.
What does 2-5 next to a fillet symbol mean?
An intermittent fillet: each weld segment is 2 inches long, and the segments are spaced on 5 inch centres measured start to start.
Welding symbol anatomy
Every weld symbol attaches to the same framework. If any part of the diagram above is unfamiliar, the full guide to reading welding symbols walks through the whole system.
| Reference line | The horizontal backbone of every welding symbol. Everything else attaches to it, and it is always drawn horizontal on the drawing. |
|---|---|
| Arrow | The leader and arrowhead that connect the reference line to the joint. The side of the joint the arrow touches is the arrow side. |
| Weld symbol | The shape that says which kind of weld is required — triangle for a fillet, V for a V-groove, circle for a spot, and so on. |
| Arrow side (below the line) | A weld symbol drawn below the reference line calls for a weld on the side of the joint the arrow points to. This is the convention that catches people out most often. |
| Other side (above the line) | A weld symbol drawn above the reference line calls for a weld on the far side of the joint. |
| Both sides | Symbols drawn above and below the reference line call for welds on both sides of the joint. |
| Tail | An optional fork at the far end of the reference line, used to reference a specification, process or procedure such as GMAW or a WPS number. |
| Dimensions | Size is placed to the left of the weld symbol; length and pitch are placed to the right. |