For parts, use the Mirror a solid option to mirror a body, including features which you cannot mirror individually.
The pattern of the body can also include work features and surface features.
- Access
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Ribbon:
3D Model tab
Pattern panel
Mirror
Mirror individual features 
- Features
- Selects solid features, work features, and surface features to mirror. If selected features have dependent features, they are automatically selected. Note: Exceptions: You cannot mirror features that operate on the entire body (all fillets, rounds, shells), and features based on the results of an intersect operation.
- Mirror Plane
- Selects a work plane or planar face across which selected features are mirrored.
- Solid
- In a multibody part, selects the solid body to receive the mirror. Not available in a single body part file.
Mirror a solid 
- Include Work\Surface Features
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Selects one or more work or surface features to mirror.
- Mirror Plane
- Selects a work plane or planar face across which selected work features, surface features, and the solid are mirrored.
- Remove Original
- Removes the original body. Only the mirrored occurrence remains in the part file. Use to model a left-hand and right-hand version of a part.
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Join - Joins the feature to the selected body.
New Solid - Creates a body in a multibody part.
(More) 
Specifies how mirrored features are calculated.
- Optimized
- Creates identical copies of selected features by mirroring feature faces. Optimized is the fastest compute method. But it presents some limitations, such as the inability to create overlapping occurrences, or occurrences that intersect different faces than the faces of the original features. Speeds up mirror compute.
- Identical
- Creates identical copies of selected features by replicating the results of original features. When the optimized method is not possible, use Identical for identical features.
- Adjust
- Creates potentially differing copies of selected features by mirroring features and calculating extents or terminations of each mirror occurrence individually. Computation time can be lengthy for patterns with large numbers of occurrences. Preserves design intent by allowing mirror occurrences to adjust based upon feature extent or termination conditions, such as a mirrored feature that terminates on a model face. Note: Not available for mirrors of solid part bodies in an open or surface state.