This things helps damp vibration (better ghosting and ringing on print) of Flsun Q5 arms with two springs every two arms (like SR model), one on tower side and the other hotend side.
There is two different design, up and down. the correct mounting is when the spring is far to fisheye.
If you want better lookin one o couple print mirrored (as an image).

I have used sprinng with these caratteristic:
-6mm of diameter
-25mm length (include loops)
-0.6mm of steel wire diameter.

Better choice for material is ABS or ASA. Probably is ok PETG.