GaugePass

Weld symbol

Fillet weld symbol

The right triangle on the reference line calls for a fillet weld. The number to its left is the leg size, and the side of the line it sits on tells you which face of the joint gets welded.

Interactive drawing

1/4
TitleFillet weld symbol
ViewAs drawn
Sheet1 / 2
The symbol as it appears on the drawing
arrowarrow sideother side
TitleFillet weld joint
ViewSection
Sheet2 / 2
The joint it produces, in cross-section

Reads asArrow side: fillet weld, 1/4 size.

How to read it

Start at the arrow. The arrow touches the joint the symbol is talking about, and the side of the joint the arrow tip lands on is the arrow side. A triangle drawn below the reference line means weld that arrow side; a triangle above the line means weld the opposite face of the same joint. Nothing about the arrow's direction, angle, or which end of the line it leaves from changes that reading.

The triangle itself is always drawn with its vertical leg on the left, no matter which way the joint faces on the drawing. That is a drafting convention, not a picture of the weld's orientation, so do not try to infer from the triangle whether the fillet leans left or right on the part. The joint sketch beside the symbol is what tells you the geometry; the triangle only tells you the weld type.

The number to the left of the triangle is the leg size. A single number means both legs of the fillet are that dimension, so a 1/4 fillet has a quarter-inch leg along the upright member and a quarter-inch leg along the base. If no number appears at all, the size is being set somewhere else - a general note, a weld schedule, or the procedure the tail points to - and you should go find it rather than guess.

A number to the right of the triangle is a length. With no length shown, the weld runs the full length of the joint the arrow points at, stopping where the joint stops. That default trips people up more than any other part of the notation, because a bare triangle with a size looks incomplete when in fact it is a complete instruction: weld this side, this size, all the way.

Where each dimension goes

Size (left of the triangle)
Leg length of the fillet, measured on the two faces that form the joint. One number means both legs are equal.
Length (right of the triangle)
How long the weld runs. Leave it off and the weld runs the full available length of the joint.
Side of the reference line
Below the line is the arrow side, above the line is the far side of the same joint.
Contour and finish (beyond the triangle)
An optional bar or arc on the outer face calls out flat, convex, or concave, with a letter for how that face is produced.

Worked examples

Each one is a drawing, the sentence it comes out as, and then the mark-by-mark account of why. Read the sheet first and say the sentence yourself before you look down.

  1. Fillet welds on both faces of a tee

    5/165/16
    TitleFillet welds on both faces of a tee
    RefFillet weld
    Ex1 / 2

    Reads as

    Weld a 5/16 fillet on both sides of the tee, full length.

    Which mark says so

    • fillet symbolBelow the reference lineA fillet weld on the arrow side of the joint
    • 5/16Left of the arrow-side symbolLeg size of the fillet
    • fillet symbolAbove the reference lineA fillet weld on the far side of the joint
    • 5/16Left of the other-side symbolLeg size of the fillet

    Two triangles, one above and one below the reference line, each carrying its own 5/16 size. Same joint, both faces. Neither carries a length, so each weld runs the whole joint.

    And what it does not say

    • No length is given, so each weld runs the full length of the joint.
    • There is no circle at the elbow, so the weld does not continue around the joint.

  2. A single fillet with a stated length

    1/46
    TitleA single fillet with a stated length
    RefFillet weld
    Ex2 / 2

    Reads as

    Put a 1/4 fillet six inches long on the arrow side only.

    Which mark says so

    • fillet symbolBelow the reference lineA fillet weld on the arrow side of the joint
    • 1/4Left of the symbolLeg size of the fillet
    • 6Right of the symbolLength of each weld

    The 1/4 to the left of the triangle is the leg size and the 6 to the right is the run length. Only one triangle appears, and it sits below the line, so the far face of the joint stays bare.

    And what it does not say

    • No pitch follows the length, so the weld is continuous over that length.
    • Nothing sits above the reference line, so the far face of the joint stays bare.
    • There is no circle at the elbow, so the weld does not continue around the joint.

Common mistakes

  • Reading the triangle's vertical leg as a picture of which way the weld faces on the part. It is drawn on the left every time.
  • Assuming a symbol with no length means the size is missing. No length means full length of the joint.
  • Welding only the arrow side when a triangle also appears above the reference line.
  • Treating the leg size as a throat dimension. Leg and throat are different measurements and the number left of the triangle is the leg.

Typical joints

Tee jointsLap jointsInside corner jointsStiffener-to-web attachments

Related symbols

Double filletA fillet triangle above and below the reference line means both faces of the same joint get welded. Each triangle carries its own size and length, so the two welds do not have to match.Intermittent filletTwo numbers to the right of the fillet triangle turn a continuous weld into a series of segments: the first is how long each segment runs, the second is the centre-to-centre spacing between them.Unequal leg filletTwo numbers separated by a multiplication sign to the left of the fillet triangle call for legs of different lengths, and the drawing has to show which leg goes on which member.Arrow vs other sideThe single fact the whole notation rests on: information below the reference line applies to the side of the joint the arrow touches, and information above it applies to the opposite side.