Merges two subdivision
surfaces to create a new subdivision surface.
Subdiv Surfaces > Attach > 
- Merge UVs Also
-
Merges the UVs shared by the edges that you attach.
If turned off, the UVs are not merged and can be manipulated and
edited independent of each other.
- Threshold
-
Any vertices further apart than this distance
will not be attached. Set this value carefully. If it’s too small,
no vertices will attach. If it’s too large, the operation may attach
vertices that you do not want attached.
- Keep Originals
-
Controls whether Maya keeps the original surfaces
you are attaching.
