I was adding ailerons to my GWS Slow Stick and needed a control horn. There are some here on thingiverse but they are all one-piece and have weakness at the layer interfaces.
I've designed this control horn to be printed in two pieces so that the layers of each piece are printed in an orientation that makes the part as strong as possible.
Print the parts, they are meant to fit together. For PLA, epoxy the two parts together. I printed mine in ABS on an Afinia H-Series printer. I quickly dowsed my horns with acetone and left them to dry outside. The acetone acts as a glue and also binds the layers together.
I made the base pad kind of large since I was planning on gluing it to my aileron. There is enough material there to drill some mounting holes.