This is a single-strand wire, AWG22, manufactured by Western Electric in the 1960s. It consists of copper wire - tin plating - plastic - paper. Personally, I think AWG22 is the best thickness for internal wiring in both electric guitars and basses. I think it's a very good way to experience the quality of Western Electric / single-strand wire. Of course, it's also worth trying a combination of stranded wire for the hot and single-strand wire for the ground. Guitar Parts