These are simple hooks for springs on the Predator Rods. Useful to reduce play on the rods.
I suggest you to attach the hooks directly on the base on the ball joint (metallic part). NOT on the arms.
The springs that Ive used was taken on Amazon, measures:
Lenght: 36,5 mm
Diameter of the spring: 25
Diameter of the ring: 5 mm
Edit: Added comparison photos of the same model printed before and after the mod. The prints are done at 90mm/s.
Edit2: Modified the holders. Now they are longer than before and does not move anymore along the rods. Now the springs (or the rebber bands) can be maintained away from the edges)
The newer versions are: Predator - Rods Springs Holder V3 Extended-1 & Predator - Rods Springs Holder V3 Extended-2 for the Left&Right positions.