(He makes his own very thin brass coil springs to run the cables through.)
https://m.youtube.com/watch?v=grgIhw1YbHw
Episode 2 link for others' reference:
https://m.youtube.com/watch?v=rhjJjDWMQOw&pp=ugUEEgJlbg%3D%3...
The magnetic hands were such a cool idea, and the way he builds the springs for the bowden cables in ep 2, gorgeous!