Choose the Symmetric command 
.
Click an existing line that you want to use as a symmetry axis (A).
Tip:
In ordered profile and sketch, you can use the Symmetry Axis command to activate a line to use as a symmetry axis before you select the Symmetry command. If you do, skip this step.
Click the first element that you want to make symmetric about the axis. (B)
Click another element that you want to make symmetric about the axis (C).
The two elements become symmetrical about the axis (D).
