May have answered my own question
Vintage spiral wound shift cable outer
https://www.veloduo.co.uk/products/vintage-spiral-wound-derailleur-cable-outer
4.5mm OD
"This is the real thing as used by Campagnolo back in the day. Use it for a
pukka vintage look. Specially made by Nissen-Cable Ltd in Japan."
.
Linked ferrules are 5mm (plain) or 3.9mm (stepped) so I'm guessing no ferrule.