Magnet circles?

[vampist]

I tried a google search but I just get electromagnets.

What would be the use of putting a magnet or a... iron circle of some sort. Around an electrical wire?
I opened up my old printer to see would I could use or salvage and I seen almost everything in there has some sort of iron or magnet (if they are magnets they are very weak) around them.

Hell even some capacitors in there have a smaller circle of iron around one lead.

 

[Atomic Rooster]

They are ferrite rings that help filter out high frequency noise.

Ferrite bead - Wiki

 

[vampist]

They are ferrite rings that help filter out high frequency noise.

Ferrite bead - Wiki

Oh wow, thank you. Never knew what the "box" was at the end of the usb cable lol.