You can form a subassembly from components (individual parts or subassemblies) that are already in the assembly, thereby moving the components down one level in the assembly hierarchy.
Before creating a new subassembly, you can specify the default behavior for saving it, either as a separate external assembly file or as a virtual component within the parent assembly file. Click and select or clear Save new components to external files.
Recommendation: Position and mate at least one of the components before you begin, then select that component first.
All the components must be at the same level within a single parent assembly.
To form a new assembly from existing components:
Example
In this example, assembly
A contains components
P1 and
P2.
P1 and
P2 are selected to form a new subassembly,
S1.
Instead of referencing the individual component documents
P1 and
P2, assembly
A now references the subassembly document
S1.

Any mates that exist between components P1 and P2 move from the Mates folder of assembly A to the Mates folder of subassembly S1.