Funnily enough I have also worked with them, but all of mine were short lengths so I have absolutely no sense of scale for what kilometres of it looks like rolled up. Or had, I suppose, until now. I just used them to run light into awkward spots for sensors, though, so I wasn’t exactly maxxing out the potential applications

By a neat coincidence I also play a bit of guitar, and a quarter millimetre is the diameter of the thinnest string on most of mine. For any other guitarists reading, a 10 gauge string is 0.254 mm