A 5mm Snap-on ferrite clip for keeping RF out of keyboards/mice and other Shack peripherals. Works wonders on keyboard/mouse lock-ups and also reducing breakthrough on "Hi-Fi" speakers. Fits nicely over RG58.
M0PZT says: "These are great for use at the feed-point of a 2m Slim-Jim when a small ferrite and only a single pass-through is required..."
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.