Rod-ends are made from four bits of plastic and a 10mm M3 screw.
The screw goes into the bulb.
Two of these ball-joints screw into the back of the eye plate and two are bolted onto servo horn extensions.
If the two halves of the ball retainer aren't flat... smack them with a bit of sandpaper on a flat surface.
Insert a ball into one half of the retainer...
And make a sammich.
Hold the two retainer halves together with an end-cap. It's a little snug... use the force.
We'll make this permanent with plastic rivets. Start by heating one end of a bit of filament until it starts to slump a bit.
Mushroom the end of the filament out on a flat surface and let it cool.
Cut the rivet to length and insert it (two of them) into the rod-end.
Heat-up the other end of the rivet.
...and your flat surface might not work here to finish the rivet. You can use a pencil eraser to shape the other end of the rivet or live dangerously and pat the plastic with the tip of your finger.
Molten plastic can stick to your skin... and when it does, it will burn. Seriously.
Repeat these steps to make a set of four... two per armature.