Metallic looking loops in some wire - what are they?

Hello everyone,

Some of the wire I strip has a knot in it, usually covered in plastic. Under the plastic is looped wire inside of a circular metallic ring. Most of them are gray but I have seen some green ones.



What type of material is the ring and what does it actually do?

I searched here and Google Images and wasn't able to find anything, so I hope the keywords in this thread help others that may be wondering.

I believe that's some sort of a dampener. It's ferrite. I just put it in with the light metal. You will also find it on tv yolks.

That is so the wire does not create rf frequencies and act as an antennae.

Thank you!! Yes, I have some from laptop power supplies that are halved like the picture and one from a tv yoke that looks like a cone.