Mirroring Geometry
Use the 
Mirror command to mirror Sketcher geometry about a linear reference, such as edges, lines, or centerlines. You can mirror construction and solid geometry. For example, you can create half of the section and then mirror it about a centerline or a straight edge.
Mirror command to mirror Sketcher geometry about a linear reference, such as edges, lines, or centerlines. You can mirror construction and solid geometry. For example, you can create half of the section and then mirror it about a centerline or a straight edge.The dimensions of one side are used to solve the other. This reduces the number of dimensions necessary to solve the section. When you mirror geometry, constraints are also mirrored.
When an entity has its end point on the top of a mirroring centerline, the entity’s end point has point on constraint with respect to the mirroring centerline. If you mirror such an entity, end point of the original entity that is on the mirroring centerline, and the end point of the mirrored entity will behave as if they have same point constraint.
 | You can mirror only geometric entities. You cannot mirror dimensions, text entities, centerlines, and reference entities. |