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What is that cylinder on cables?

What's this part?

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3 Answers 3


It is a Ferrite Bead.

They're used to reduce and dissipate high frequency noise.

To prevent it from moving on the cable, it is overmoulded with plastic.

Functionally, it is a dissipative low-pass filter. It's basically an inductor with very high reluctance, so the magnetic field which it forms get dissipated as heat, rather than reflected back on the cable.

  • Why is high frequency noise a problem on a laptop power cable?
    – jwg
    May 15, 2014 at 9:26
  • 1
    @jwg - Because laptops are excellent sources of it! It's actually more to prevent the laptop radiating electromagnetic noise then receiving it.
    – Fake Name
    May 15, 2014 at 9:48

It could be a recording device disguised as a USB cable.


The device in your picture is most likely a ferrite ring and is used to reduce RF interference. You'll also see them on a lot of video cables.

You can also buy them as a separate item

Have a look here

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