A 13mm Snap-on ferrite clip for keeping RF out of keyboards/mice and other Shack perhiperals. A few loops of a cable around these can work wonders on keyboard/mouse lock-ups and also reducing breakthrough on "Hi-Fi" speakers. Can be used on RG58/RG213 coaxial cable. You can obviously use more than 1 on a cable if you have a particularly tricky RFI issue!
If you plan on using snap-on ferrites on coaxial cable (especially at HF frequencies), it's advisable to use a proper 31-mix Fair-Rite core such as the Problem Solver... Or, for smaller cables, Aerial Parts of Colchester sell these.