Hi

I used this one which is readily available ( I think it is by Sullivan).
It is a simple thick nylon affair but after 50 hours in my CG Chipmunk it is still fine.
I have kicked rudder (by accident) and cracked the rudder by bumping it against the boot (trunk??) while packing it in and the servo gears have not been damaged.

It has the "Ackerman" (rotary to linear differential ??) built in - ie the holes are offset.