White felt rings around balls of Pirastro strings

[Calvin Marks]

What are these white felt rings at the ball-ends of Pirastro strings? I never install them...What exactly are they?

Thanks.

[Jeff Bollbach]

White felt rings around balls............... I know, too easy. These guys ameliorate damage and/or wedging as the ball end pulls into the slot under tightening. Some claim they have an effect on the actual sound but I have never noticed this.

[Greg Clinkingbeard]

I have an old string where the wire loop that goes over the ball broke. That string wasn't using the proper protection when it wedged tightly into the slot.