Short answer: A welding symbol is a shorthand on the drawing: a reference line carries the arrow to the joint, a weld-type symbol above or below shows the joint (fillet, groove, plug), and numbers give size, length and pitch — so reading it tells you exactly what weld to make and where.
At a Glance
Anatomy of a Welding Symbol
The reference line is the backbone: the arrow points to the joint, and anything drawn on the arrow side sits below the line, on the other side above it. A flag at the tail means field weld; specifications live in the tail. This notation is what welders follow when executing How To Weld Stainless Steel, How To Weld Carbon Steel en Aluminium lassen.
Fillet, Groove & Special Symbols
The triangle is a fillet weld (size = leg length); a V or bevel is a groove weld for full-penetration butt joints; square groove suits thin stock; plug and slot welds transfer shear; the seam circle marks resistance/spot welding common in sheet and auto bodies. Every symbol must avoid the defects catalogued in Weld Defects Guide, and dissimilar metals follow Dissimilar Metal Welding Guide.
Size, Length & Inspection
Numbers on the symbol give leg size, weld length and pitch (for intermittent welds); a circle at the junction means all-around. Inspect to the callout with the methods in Metal Ndt Guide and verify the joint matches the design intent. Misreading a symbol is a top cause of field rework, so the symbol is the contract between designer and welder.
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The triangle (△) is a fillet weld; the number beside it is the leg length. It is the most common symbol for T-joints and lap joints.
Weld symbols below the reference line apply to the arrow side of the joint; symbols above apply to the opposite side. Both sides means a weld on each.
An all-around weld — the weld runs continuously around the entire joint perimeter.
Groove symbols (V, bevel, square, U) specify butt and corner joints for full-penetration welds, with the angle and root opening noted on the drawing.
HXSCO supplies plate, pipe and sections with certified chemistry for welding and can advise on grades; filler guidance is in our welding consumables resources.
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