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What is that cylinder on cables?

What's this part?

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marked as duplicate by Sathya, Joe Taylor, AndrejaKo, Arjan, Dennis Williamson Jan 17 '11 at 10:53

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3 Answers

up vote 10 down vote accepted

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.

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

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+1 for urban myth potential :) –  Sirex Jan 17 '11 at 10:19
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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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