Ferrite rings are used for fixing on cables, when laying them in places with high level of electromagnetic interference. Recommended for audio and video cables. An open ferrite cylinder is placed on the cable to be protected from electromagnetic interference, approximately 1.2 inches from the cable lug. A loop is made around the sheath of the cylinder. The sheath is then snapped into place. The other end of the cable can also be fitted with a ferrite cylinder for reliability.