All aluminum cable. There is no steel wire in the cable. Aluminum wire is not as conductive as copper but it is much lighter. To achieve the same conductivity as copper, thicker aluminum wire must be used. Overhead transmission lines are already constructed exclusively with aluminum. The reason is weight. If they were built out of copper you would need super-sized pylons to hold them up. When copper prices rose in the mid-1960s, aluminum wire was manufactured at a gauge small enough to be used in homes. Aluminum wire was blamed for a number of house fires that were caused by faulty connections. a U-670. The incuse markings of ICTO inside the outline of a multipart are incomplete as the complete name would be VICTOR Not in my collection any more.