X-Tech Large Base Control Horn With Ball Raced Head & Clevis 25MM. These horns are designed to be screwed to the control surface (usually plywood set into & glued to the surface) with the three screws provided. Because of the large area of the plastic base the torque is transferred over a larger area. The base of the horn has the mounting of the alloy transfer arm angled towards the hinge line to aid the geometry of the overall control linkage. To ensure the linkage is slop free, the clevis pin runs through a miniature ball race rather that just plain plastic which in time would wear & end up with slop.