Maybe this community is not the right one for this question, but I was curious why some cable have these cylindrical parts (like the one in the photo.)
What are they and what is their purpose?
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They are [ferrite beads](https://en.wikipedia.org/wiki/Ferrite_bead). Also, [Does the position of the Ferrite bead matter?](https://electronics.stackexchange.com/q/111495/36731) – Andrew Morton Apr 16 '22 at 13:55
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3As mentioned already, they **might** be ferrite beads to make cables radiate less and make them perform better, but they **might** also be just plastic lumps to make a garbage cable look more expensive and professional by faking the look it actually has ferrite beads. – Justme Apr 16 '22 at 14:15
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That is a clamp-on ferrite high-frequency noise filter. Effectively, it is a thick-walled cylinder of iron ferrite that has been sliced down its axis to form two halves. The halves are in a plastic case that snaps around a cable, re-forming the cylinder. The ferrite acts as a wad of inductance, which works with the cable's natural capacitance to form a low-pass filter.
This is common on data cables and switching power supply cables to attenuate generated noise and the very-high frequency components of signals from radiating and causing interference with other devices.
AnalogKid
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More specifically, it's a common mode choke. These chokes (filters) attenuate high frequencies that flow along all of the wires in the cable.
They are usually a band aid approach to meeting some EMC requirement. A well designed piece of electronics should not need them on external cables.
SteveSh
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