The weld symbol is unique in the Structural Detailing task because it is a FT Visual Basic symbol instead of a 2D RAD symbol and does not have any geometric representation in the model; it is only used to hold parameter values.
The FT_WeldSymbols.vbp Visual Basic project can be found in the [Programming Resources Folder]\Programming\ExampleCode\StructDetail\Symbols\FT_WeldSymbols folder.
Most Parameter Names Defined in the Symbol Cannot Be Changed
The weld symbol must also handle the properties and parameters defined for IJWeldingSymbol. These property names are defined in a virtual interface definition within the schema and cannot be changed without impact to anyone that uses them.