You can create opposite-hand versions of selected components by mirroring about a selected plane. Optionally, you can constrain the original and opposite-hand components to remain symmetrical about the plane.
From the Assembly section of the action bar, click Mirror Component.
For Mirror Plane, select a plane or planar face.
For Components to Mirror, select one or more components from the main level of the current assembly.
To keep the components symmetrical to each other about the mirror plane, click Symmetric Constraint. Otherwise, the components can move independent of each other.