Mechanical structure, by design, enables you to group geometries as parts and assemblies (components), independently of the BOM.
When you insert a component in the drawing area, the BOM updates automatically.
In addition to the main BOM, you can create BOMs for any assembly within the mechanical structure. The assembly BOM contains only the parts and sub assemblies contained within that assembly.
When you create a component, an entry is automatically added to the BOM. You may, however, want to do the following:
In some cases, parts and assemblies are included in a drawing to provide context to a drawing. Such parts and components should not be included in the BOM. To exclude them from the BOM, you flag them as Reference Components. Reference Components are automatically excluded from the BOM.
In some cases you want to keep an item in the BOM, but exclude it from parts lists only. To do this, display the properties of the component and select the relevant option to exclude it from all parts lists.
In some cases, you do not want to draw all occurrences of a part in an assembly. In such a case, select the part and override its quantity so that the BOM shows the actual number of parts belonging to the assembly, instead of the number of parts drawn in the drawing area.
At the time you create a new mechanical structure component, the BOM only captures the name of the component. You set the other component properties manually. Once the properties are specified for one instance of a component, all instances are automatically updated. Whenever you place new instances of this component in model space, the new instances automatically contain the information you entered.