You can extract polygons to create a new object based on selected polygons of an existing object.
Extract Polygons (delete) creates a new object and removes the selected polygons from the original object.
Unlike most modeling operations, this does not maintain a modeling relation with the original object — in other words, modifying the original object after you have used this command does not affect the extracted object.
If you don't want to create a new object but instead want the separated polygons to remain part of the original object, you should disconnect the polygons instead of extracting them. For more information, see Disconnecting Polygon Mesh Components.
Extract Polygons (keep) creates a new object but leaves the selected polygons on the original object.
If you don't want to create a new object but instead want the duplicated polygons to be added to original object, you should duplicate the polygons instead if extracting them. For more information, see Extruding, Duplicating, and Insetting Polygon Mesh Components.
Clusters with the following properties are automatically transferred to the generated object: materials, texture UVs, vertex colors, property weight maps, envelope weights, and shape animation. Creases, hard edges, and hard vertices are also propagated. By default, the Extract operators connect at the top of the input object's construction stack (see Choosing the Connection Point). If you want to change the connection point, look up ChangeGeneratorInputReadPosition and related commands in the SDK Guide.
Select one or more polygons or polygon clusters on a polygon mesh object.
Do either one of the following:
If you want to delete the polygons from the original object, choose Create 
Poly. Mesh Extract Polygons (delete) on the Model toolbar.
If you want to keep the polygons on the original object, choose Create Poly. Mesh Extract Polygons (keep) on the Model toolbar.
New objects are created as follows:
If you selected polygons or a single cluster in step 1, a single new object is created, named either polymsh_extracted (if you kept the original polygons) or polymsh_detached (if you deleted them).
If you selected multiple clusters, each cluster creates a separate object named either polymsh_extracted, polymsh_extracted1, polymsh_extracted2, and so on, or polymsh_detached, polymsh_detached1, polymsh_detached2, and so on. These new objects are children of a new null called polymsh_extracted_null or polymsh_detached_null as appropriate.
This also occurs if you select a combination of clusters and polygons. The selected polygons are treated as if they were a single additional cluster.
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