What is this called?

[Devante]

Some cords that come with electronics have some type of piece on one of the ends that houses some type of metal (I can't tell if it's a magnet or just iron or something).

I believe, if I'm not mistaken, that the PS2 controllers have this near the end you plug into the console.

One time I bought a video camera that came with a recharging cable that had the piece seperate from the cord.
The instructions directed you to clamp the piece (which was a cone of metal surrounded by a plastic shell) onto an end of the charging cable.

For some reason, this USB cable I found has one of these pieces on one end, I'd like to remove it but want to know what it is, first.

What is this piece called?
What does it do?
Is it necessary?



Thanks!



:: edit ::

Not 5 minutes later did I realize these were ferrite clamps.

But what do they do exactly?
And what is one doing on a USB cable?

 

[Veho]

It's a passive lowpass filter (fancy name for a piece of magnet that you loop your cable around). It dampens the electronic noise and electromagnetic interference from nearby electrical cables, mains and devices. You can take it off with no ill effects.