The screened wire core was made of a bi-filar wound string with about 2 turns per inch with each wire forming one of the secondaries. The primary screen was made from sections of tinned copper braid about 3" long that were soldered together to form a continuous screen. With tinned copper braid, poking a screwdriver down the end pushes the strands out to form a tube that can be slid over the wires used as the core. You are limited to the maximum length by how long your screwdriver is but these sections can be soldered together to form one long screen around the secondary wires. The lot was insulated with black electrical insulating tape.