Free reference
Weld symbol reference
Every symbol you will meet on a fabrication drawing, 40 pages in all. Each one has an interactive drawing you can flip between arrow side and other side, a reading guide in plain English, worked examples, and the misreadings that cost money.
How to use these pages
The whole notation hangs on one fact: information below the reference line describes the side of the joint the arrow touches, and information above it describes the other side. Start with arrow side versus other side if that sentence is new, then come back for the individual symbols.
Fillet welds
5 pagesFillet weldThe 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.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.Staggered intermittentIntermittent fillets on both faces of a joint, offset so a weld on one side sits opposite a gap on the other. The two triangles are drawn out of line to signal the offset.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.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.
Groove welds
16 pagesSquare grooveTwo short parallel lines crossing the reference line call for a square groove weld — a butt joint welded with no bevel, where the only preparation is how far apart the two square edges are set.V-groove weldA V drawn on the reference line calls for a V-groove weld. Both members are bevelled, and the symbol carries three numbers: the included angle, the root opening, and the depth of the groove.Double V-grooveA V above and below the reference line prepares the joint from both faces, giving an X-shaped cross section that halves the weld metal of a single V on thick material and balances shrinkage.Bevel grooveHalf a vee — one vertical leg and one sloped face — means only one member is prepared. A broken arrow points at the member that gets the bevel, because the symbol alone cannot say.Double bevelOne member bevelled from both faces while the other stays square, giving a K-shaped cross section. Two half-vee symbols sit on the reference line, one above and one below.U-groove weldA U-shaped symbol calls for a groove with curved, near-vertical prepared faces and a radiused root. It uses far less weld metal than a vee on thick material but has to be machined or gouged.Double U-grooveU-shaped preparations on both faces of a butt joint, drawn as a U above and below the reference line. It is the lowest-volume preparation available for very thick, two-sided access.J-groove weldHalf of a U: one member is machined to a curved, near-vertical face with a radiused root while the other stays square. A broken arrow shows which member gets the preparation.Double J-grooveOne member machined to a J profile from both faces while the other stays square. Two half-U symbols sit on the reference line, and the broken arrow still shows which member is cut.Flare V-grooveTwo outward-bowing curves mean the groove is formed by the natural radius of two rounded members set together — no cutting involved, since the parts themselves create the vee.Flare bevel grooveOne straight member against one rounded one. The symbol shows a vertical leg and a single outward curve, and the groove is formed by the radius of the curved part rather than by any cutting.Back weldA semicircle opposite a groove symbol calls for a weld deposited on the back of the joint after the groove side is welded, sealing and reinforcing the root from the far face.Backing weldThe same semicircle as a back weld, but deposited first. A backing weld is laid in the root before the groove is filled, giving the groove side something solid to fuse into.Backing barA rectangle or semicircle opposite the groove, with a letter noting whether the backing is removed, says a separate piece of material sits behind the root while the groove is filled.CJP groove weldCJP in the tail says the weld must fuse through the entire thickness of the joint. The preparation is left to the fabricator, so no groove size appears to the left of the symbol.PJP groove weldA groove weld deliberately not carried through the full thickness. Numbers to the left of the symbol give the depth of preparation and, in parentheses, the effective throat the design relies on.
Plug and slot welds
2 pagesPlug weldA rectangle open toward the reference line calls for a plug weld: a hole made in the near member and filled with weld metal to join it to the member underneath.Slot weldThe same open rectangle as a plug weld, but the hole is elongated. Because a slot has length, width, orientation, and end radii, much of its geometry lives on the drawing.
Resistance welds
4 pagesSpot weldA circle on the reference line calls for spot welds: individual fused nuggets made between overlapping sheets, dimensioned by nugget diameter or strength, how many, and how far apart.Seam weldA circle with a bar through it calls for a seam weld — a continuous or closely overlapping resistance weld made by rolling wheel electrodes along the joint instead of stopping at each spot.Projection weldA resistance weld located by an embossed dimple or raised boss rather than by the electrode. The circle sits on the side of the reference line carrying the projections.Stud weldA circle crossed through calls for stud welding: a threaded or headed stud fused end-on to a surface in a single arc or resistance cycle, always on the arrow side.
Surfacing and edge welds
2 pagesSurfacing weldTwo scalloped bumps on the reference line call for weld metal deposited onto a surface rather than into a joint. The size to the left is the thickness of the deposit, not a joint dimension.Edge weldTwo parallel lines calling for a weld along the abutting edges of parts lying face to face. It shares its glyph with the square groove, and only the joint the arrow points at tells them apart.
Supplementary symbols and notation
11 pagesWeld all aroundA circle at the elbow where the leader meets the reference line means the weld continues completely around the joint, wrapping every side of the attachment rather than stopping at a corner.Field weldA flag at the elbow says the weld is made in the field rather than in the shop. It is a scheduling and quality instruction, not a change to the weld itself.Melt-through symbolA filled semicircle on the far side of the reference line calls for visible root reinforcement pushed completely through a joint welded from one side only.Flush contourA straight bar drawn across the outer face of a weld symbol calls for the finished weld face to be level with the adjoining surfaces rather than left with its natural reinforcement.Convex contourAn arc bowing away from the reference line calls for a weld face that stands proud of a straight line between its toes, giving extra metal in the middle of the bead.Concave contourAn arc dishing back toward the reference line calls for a weld face that curves inward between its toes, easing the transition into the base metal at the cost of throat thickness.Finish methodsA single letter written with a contour symbol names how the weld face is brought to that shape — grinding, machining, chipping, rolling, hammering, or an unspecified method.The tailThe forked tail at the far end of the reference line holds information the symbol itself cannot carry: the process, the procedure, the consumable, or a note the joint depends on.Reference line basicsEvery welding symbol is built on one horizontal reference line with an arrow at one end and an optional tail at the other. Where information sits on that line is what gives it meaning.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.Multiple reference linesStacked reference lines on one arrow spell out a sequence of operations. The line nearest the arrow is done first, and each line further out is done after the one before it.