You can make a single part out of 2 or more parts that have overlapping geometry and are of the same material. The merged part can be edited to add or remove parts. The edit mode for merged parts is also available when you are in Edit Division mode and the selected division includes merged parts. When you have a complex hierarchy of part divisions and part merges, these edit modes are nested within each other as needed to support recursive editing.
To create a merged part
- Select the parts to be merged.
- Click Modify | Parts tab
Part panel 
(Merge Parts).
To edit a merged part
- Select the merged part.
- Click Modify | Parts tab (or Modify | Division if you are already editing a division that contains a merged part) Part panel
(Edit Merged). - Click Modify | Merged Part tab Merged Parts panel
(Add) or 
(Remove), and then select the parts to be added or removed. - When finished adding or removing parts, click
(Finish Edit Mode).
To edit a merged part that is included in a division
- Select one of the parts that resulted from the division.
- Click Modify | Division Part panel (Edit Merged).
- Select the merged part.
- Click Modify | Merged Part tab Merged Parts panel (Add) or (Remove), and then select the parts to be added or removed.
- When finished adding or removing parts, click (Finish Edit Mode).