What is the name of the oblong black shell thing that is (presumably) connecting the two halves of the cable? There is a small one and a large one shown in the image below.

I've searched around for electrical cable connectors/joiners, but haven't been able to find this exact part. They seem pretty common, I have seen a few on USB cables I have.

I'd like to buy some of these for a project, so if you know what to search for on eBay to find these, I'd appreciate it.

EDIT: Thank you for the answers. I was actually looking for some sort of in-line compartment to hold a little circuit, and was surprised to learn about ferrite cores.

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image source

  • \$\begingroup\$ A ferrite on an external cable is almost always added as a last attempt to get the equipment to pass an EMC requirement. Also used in making antennas, chokes, transformers. Based on your question though, you are very unlikely to need one to make a project work; they don't affect the signal in the wire, only the common mode currents. So unless you're already testing in an EMC chamber, or have other radio interference, don't worry about adding beads. \$\endgroup\$
    – tomnexus
    Commented Apr 2, 2015 at 5:42

2 Answers 2


That is actually a ferrite core. It helps remove noise from the wires that are run through and looped around it, the wires are not joined in the middle of it. Basically they are just used for signal integrity and interference issues and can be clipped on to existing cabling if there are such problems.

Check a listing out here. They come in all sorts of shapes and sizes so be sure to get one that is suitable for your cabling.


As others have noted, the two obvious oblong shapes are ferrite cores. However, there is also a moulded cable junction in the picture, hidden under the cable a little, if that is what you actually need.

For small signal cables made in large volumes at low cost, these are usually custom moulds made by the cable company assembling the cable. For larger cables (e.g. mains cables etc) there are standard products from 3M and others (here is a picture from CBI cables)

If appearance is not critical, you can create your own mould, connect and test the conductors, add some strain relief if possible, and use 'potting compound' (commonly epoxy, silcone or polyurethane) to enclose and protect the join.

  • \$\begingroup\$ that IS actually what I needed, thanks for this answer rolinger \$\endgroup\$
    – Aralox
    Commented Apr 3, 2015 at 2:28
  • \$\begingroup\$ @aralox, happy to help, will you change the accepted answer? meta.stackoverflow.com/questions/251078/… \$\endgroup\$
    – rolinger
    Commented Apr 3, 2015 at 13:10

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