When I built the elevators and the horizontal stabilizer, I didn't fit them together by drilling either the top or bottom elevator horns. These horns are best dirlled with the elevators mounted to the stabilizer. The holes must be exactly perpendicular to the horns or when the bolt installing the pushrod is tightened, one horn will be pulled forward and the other aft, mis-aligning the counterbalance arms on the elevators. Since I can't do this on a drill press, I decided to clamp the counterbalance in place and drill two holes for two bolts; one for the push-pull pivot and one to keep the horns parallel.