You can place features symmetrically on a part. It can be helpful to define the bisector of a sketch and constrain or dimension geometry relative to the bisector so that the sketch updates relative to the part.
Share the sketch , and then dimension feature sketches to the midplane line. You can use equations to constrain feature size and location relative to one another.
Locate the midplane by sketching a line from the midpoint of one side to the midpoint of the opposite side. To begin, use commands on the Sketch tab to create sketch geometry. In an active sketch:
Because the line is constrained to the midpoints, it stays in the center of the sketch if it changes size.