Detach Assembly
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Select an assembly. Group menu Assembly Open Select one or more objects to detach. Assembly Detach

Select one or more objects to detach in an open assembly. Group menu Assembly Detach

The Detach command detaches the selected object from its assembly. If the object is a member of a nested assembly, after you detach it, it is no longer a member of any assembly.

This command becomes active when you open the assembly by choosing Open from the Assembly menu.