Sources and scope for this page: Industry convention — no single governing standard (conventional usage, definitions vary between sources), covering the definition of weld symbol. No independent source check is recorded for this page: the content rests on the sources listed and on the working shown on the page. How sources, methods and updates are recorded.
Definition
A welding symbol has a reference line, an arrow pointing to the joint, and the symbol itself. Symbols above the reference line apply to the side the arrow points at; symbols below apply to the other side. A circle at the junction means a weld all round; a tail carries the process specification.
Fillet and groove welds have their own sizes: a fillet weld's size is its leg, and the symbol places it to the left of the letter.
Common misuse
Reading the size on the wrong side of the reference line, which specifies the weld on the wrong face of the joint.