Source of materials was my box of
Those are computer motherboard spacers.
Placed it in a vice, and hold it with a piece of soft wood.
Then a spacer is put into a drill secured tightly to working surface.
This way I used a drill as a sort of mill.
Part of the spacer with thread is filed down to smooth surface and
a groove is made, like one on the lower picture.
A hole in servo arm is made wider so newly made tip of link stopper can snuggly fit into.
After that, a small bolt is screwed in to make a grip onto steel wire used as control surface link.