523877 is a genuine Sennheiser spare part.
It suits a variety of HD25 headphones (not the ‘SP’ or budget version).
This spare cable for HD25 is coiled, and is approx 1m when sitting there, doing nothing. If you want to get stretchy with it, the cable is appox 3m.
Copper cable with 3.5mm threaded straight jack plug.
Package includes the very handy 543684 screw-type 3.5mm socket to 6.35mm jack adapter.