To Insert a Component View Into an Existing Instance of a Component (AutoCAD Mechanical Toolset)

Click Structure tabTools panelStructure Catalog. Find
From the Current Drawing tab, in the Definitions Panel in the Mechanical Structure section, right-click the component view you want to insert.
From the right-click menu select Insert as View of.Name of component you want to insert this as a view of.
Move the cursor to the position you want to insert the geometry and click.
Press Enter to accept the default rotation angle or specify a rotation angle and press Enter.
The component is inserted and is shown in the mechanical browser.

Tip:

You can also copy components from other drawings by:

Copying the component to the clipboard and pasting it in the appropriate drawing.
Importing the definition of the component using the Structure Catalog and inserting instances after that.