To Set a Symbol in the Library as the Default Symbol (AutoCAD Mechanical Toolset)

1. In the drawing area, double-click a symbol of the type of symbol library you want to edit. For example, to set a default symbol for the welding symbol library, double-click a welding symbol.
2. In the library, click the symbol to set as a default.
3. From the drop-down menu on the right, select Set default. A blue tick is displayed in front of the default symbol.
4. Click OK.