I made an extension to a servo horn, for my radio controlled plane.
Dad has got some suitable small screws, which self-tap into the plastic servo horn.
I made the thing out of aluminium. I cut the outside shape with a 3mm slot-drill, and the holes with a 1mm slot-drill. I had to work for a few days on my HeeksCNC software, so that I could fit tangential arcs from lines to circles and from circles to circles to make a smooth shape.