Its FAIR-RITE 2643004801 FERRITE CORE, CYLINDRICAL, 31OHM/100MHZ, 300MHZ, its ferrite cable core which is used to suppress the common mode noise from the power line, means in power transmission cables generate the electrical noise or noise by this can clean the common mode noise. Its used to suppress the electromagnetic emission which is emitted by the Power cables by blocking the low frequency signal.