Fillet Weld Symbol
The fillet weld symbol is a small right triangle drawn on the reference line, with its vertical leg always on the left. Below the line it means a fillet on the arrow side of the joint, above the line on the other side, and on both sides for a fillet on each side. The leg size goes to the left of the triangle and the length and pitch to the right.
How to read the fillet weld symbol
A fillet weld joins two surfaces at roughly a right angle, as in a T-joint, lap joint or corner joint, with a triangular cross-section of weld metal. The symbol copies that shape: a right triangle whose vertical leg is always drawn on the left, whichever way the arrow points.
Side is read from the reference line, not from where the arrow points on the drawing. Triangle below the line: weld the side of the joint the arrow touches (arrow side). Triangle above: weld the opposite side (other side). One triangle on each side of the line: weld both sides, which is the double fillet common on T-joints.
What each dimension position means
| Position | Meaning |
|---|---|
| Left of the symbol (S) | Leg size of the fillet. Two numbers such as 1/4 × 3/8 mean unequal legs; the drawing shows which leg is which. |
| Right of the symbol (L) | Length of the weld. No length means weld the full length of the joint, between abrupt changes in direction. |
| After a hyphen (P) | Pitch: centre-to-centre spacing of intermittent segments. "2-6" means 2-inch segments on 6-inch centres. |
| Tail | Process, filler or a specification reference, such as GMAW or a WPS number. Left off when not needed. |
Example callout, read aloud
“Weld a 1/4-inch fillet on the arrow side, in 2-inch segments spaced 6 inches centre to centre, using gas metal arc welding.”
Example: reading the callout piece by piece
- Triangle below the line: arrow side only.
- 1/4 to the left: leg size 1/4 inch.
- 2-6 to the right: intermittent welds 2 inches long at a 6-inch pitch. On a 26-inch joint that is 5 segments: (26 − 2) ÷ 6 + 1 = 5.
- GMAW in the tail: gas metal arc welding.
Result: Weld a 1/4-inch fillet on the arrow side, in 2-inch segments spaced 6 inches centre to centre, using gas metal arc welding.
When it is used
- T-joints and lap joints in brackets, frames, gussets and base plates, where no edge preparation is wanted.
- Intermittent (stitch) fillets on long joints that need stiffness but not full strength, to cut heat input and distortion.
- Double fillets on both sides of a T-joint when the load can come from either direction.
Common mistakes
- Reading side from where the arrow points on the view. Side comes from the reference line: below is arrow side, above is other side.
- Drawing the vertical leg on the right. The perpendicular leg is always on the left, whatever the arrow direction.
- Confusing size with throat. The number on the left is the leg size unless the drawing says otherwise. Throat is smaller, about 0.7 × leg for an equal-leg fillet.
- Reading 2-6 as 2 inches gap and 6 long. Length first, then pitch (centre to centre).
- Oversizing "to be safe". Weld metal grows with the square of the leg size. A 3/8 fillet has more than twice the metal of a 1/4.
Related weld symbols
- Weld-all-around: Add the all-around circle when the fillet runs right round a tube or plate.
- Field weld: Add the flag when the fillet is made on site instead of in the shop.
- Bevel groove weld: A bevel groove is the upgrade when a T-joint needs full penetration.
- Plug and slot weld: Plug and slot welds join lapped plates through holes instead of along edges.
- Edge weld: Edge welds join the edges of thin parallel sheets.
Every weld symbol page: welding symbols chart
Calculators and further reading
Frequently asked questions
Which side is the arrow side on a fillet weld symbol?
The side of the joint the arrow touches. A triangle below the reference line means weld that side; above the line means the opposite side.
What does the number to the left of the fillet symbol mean?
The leg size of the fillet weld. Two numbers mean unequal legs.
What does 2-6 mean on a fillet weld symbol?
Intermittent fillets, 2 inches long, spaced 6 inches centre to centre.
What does a fillet symbol on both sides of the line mean?
A double fillet: weld both sides of the joint. Each side carries its own size and length.
What if there is no length on a fillet weld symbol?
Weld the full length of the joint, up to abrupt changes in direction, unless the all-around symbol or a note says otherwise.
Sources
- AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination, American Welding Society
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