These compact sized Toroid Ferrite cores are useful for suppressing EMI/RFI. Applications range from audio/video equipment wiring, R/C installations, and much more.

 

Outside diameter is 0.4 inch (10mm) and inside diameter is 0.24 inch (6mm). A tough epoxy conformal coating helps reduce breakage. Colors may vary (blue, white, or black).

 

For typical common mode EMI/RFI suppression you need to wrap several turns of cable around the bobbin shaped core. Generally speaking, more turns = more suppression. Because of their small size, these Toroids are used with small gauge wire (30 AWG and higher).

They aren't effective in every electrical noise situation, but they are the first line of defense when EMI/RFI problems are encountered. Every tool box should have several of these on hand for those RF special projects that suffer from interference problems.