What are those metal donuts that wires wrap through / around

I have no idea what these things are called so I don't know what
terms to search on to research them.

Anyway, it looks like a metal donut that a paired set of wires wrap
around and through multiple times.

Questions:

1. What is it called?
2. What purpose does it serve?

Thanks

-Marcus

 

[BobG]

1. What is it called?
2. What purpose does it serve?
============================

1) ferrite bead
2) Its an inductor. Blocks hi frequencies, passes lo frequencies

 

[dB]

"BobG" <bobgardner@aol.com> wrote

1) ferrite bead
2) Its an inductor. Blocks hi frequencies, passes lo frequencies

Or a transformer.

 

Thank you all for your responses. It was exactly what I was looking
for.

Roger Johansson wrote:

BobG wrote:

1. What is it called?
2. What purpose does it serve?

1) ferrite bead
2) Its an inductor. Blocks hi frequencies, passes lo frequencies

It can also be called a _core_ for a toroid inductor, or a core for
a transformer, if more than one winding is used.

An information page for beginners about beads, toroid cores,
transformer cores, scroll down to see pictures:
http://sound.westhost.com/xfmr2.htm

This is one of the most known makers of toroid cores
http://www.amidoncorp.com/product.htm


--
Roger J.