My Delta without those was really noisy as the arms vibration was noisy and print ended up with a lot of wavy line. Than I made this little hooks for rubber band. On the picture there are 2 of them but this is not required if use the right amount of rubber band on the arms. This improve print quality and reduce noise created by vibration.
Quite small item to print make sure you go slow and thin layer layer height no more than 0.2 if you want an usable hook that will not snap by the force of the rubber band.