You can specify the mirroring plane by aligning the objects with a specified plane or by specifying three points.
It is recommended that you use the gizmos available through the 3DMOVE, 3DROTATE, and 3DSCALE commands to manipulate 3D objects.
Select the objects you want to mirror and press Enter.
Uses the plane of a selected planar object as the mirroring plane.
Delete Source Objects
If you enter y, the reflected object is placed into the drawing and the original objects are deleted. If you enter n or press Enter, the reflected object is placed into the drawing and the original objects are retained.
Mirrors the selected objects about the last defined mirroring plane.
Defines the mirroring plane by a point on the plane and a point normal to the plane.
Aligns the mirroring plane with the viewing plane of the current viewport through a point.
Aligns the mirroring plane with one of the standard planes (XY, YZ, or ZX) through a specified point.
Defines the mirroring plane by three points. If you select this option by specifying a point, the First Point on Mirror Plane prompt is not displayed.