Steel-core aluminum stranded wire is composed of aluminum and steel wires twisted together, suitable for overhead transmission lines. It has a steel "core" internally, with aluminum wires twisted around the steel core externally; the steel core primarily serves to enhance strength, while the aluminum stranded wire is mainly responsible for transmitting electrical power. For high-voltage transmission lines, due to the limited path, it's not feasible to lay multiple lines on a single path, so people came up with the idea of using one tower for a single path and hanging multiple conductors, effectively making one line equivalent to multiple lines. For 500KV transmission lines, China mostly uses the method of hanging four conductors, which is called "parallel laying on the same tower."