Dude, wtf, stop posting 10 threads with the same question! Place the pivot on the side where you want to the head to mirror. Hold 'v' while moving the pivot point and it will snap to vertex. Or if the centrev of the head is on the grid axis you can hold 'x' to snap to to grid. well if no one post in a thread i assume im in the wrong section so post in another sorry im new here