Welding symbols (ISO 2553)
A welding symbol is a compact diagram on a technical drawing that tells the welder exactly which joint to make, where to make it, and how. It is built from a small set of standardised parts that can be combined to describe almost any weld.
Anatomy of a welding symbol
Every ISO 2553 welding symbol is built around an arrow line that points to the joint and a horizontal reference line that carries the information.
Arrow line
Points from the symbol to the joint on the drawing. The direction matters — see 'arrow side' below.
Reference line (solid)
Horizontal line that carries the main weld symbol. Anything drawn on this line refers to the arrow side.
Identification line (dashed)
Drawn above or below the reference line. Carries information for the opposite side of the joint.
Weld glyph
A small shape (V, triangle, U…) placed on the reference or identification line. Tells you the type of weld.
Dimensions
Numbers around the glyph give throat thickness, leg length, root gap, included angle, length, pitch, etc.
Tail (optional)
A forked end of the reference line used to reference the welding process, standard or filler.
Arrow side vs other side
Arrow side
Glyph drawn on the solid reference line — the weld is on the side of the joint the arrow points to.
Other side
Glyph drawn on the dashed identification line — the weld is on the opposite side of the joint.
Both sides
Glyphs drawn on both lines (mirror image) — weld on both sides of the joint.
Common weld glyphs
Each glyph corresponds to a specific weld or edge preparation.
Fillet weld
Right-angle triangle. The most common weld symbol on structural drawings.
V groove
Symmetrical V. Both edges beveled, welded from one side.
Square (I) groove
Two short parallel lines. Straight edges with a small root gap.
Single bevel
Only one edge beveled — common in T-joints.
V with root face
V groove with a horizontal bar at the bottom to indicate a root face.
U groove
Curved U shape — used for heavy plate to save filler metal.
J groove
Half U — only one edge prepared with a J profile.
Flare-V
Two opposing curves for rounded edges meeting (e.g. tubes).
Edge weld
Solid rectangle on the reference line.
Plug / slot weld
Filled rectangle representing weld metal through a hole or slot.
Supplementary symbols
Weld all around
Open circle at the intersection of arrow and reference line — weld continues around the entire joint.
Field / site weld
Filled flag at the same intersection — weld is to be made on site, not in the shop.
Flush finish
Straight bar above the glyph — weld surface to be ground flush.
Convex finish
Curved bar above the glyph — weld face is convex.
Concave finish
Inverted curve — weld face is concave.