Litz tonearm wire in a traditional silk covering. Sold as a fixed 1 metre length, enough to rewire one tonearm & possibly two, depending on the arm and how the wire is used.
The set is four separately coloured wires: both channels, signal & return, for a full rewire from the cartridge tags to the base of the arm. Each 0.3mm wire carries 7 strands of Ø0.07mm high purity copper, enamel coated.
The silk needs removing before you can tin the copper. The best way is a solder pot: burn the silk away, scrape off the residue with a fingernail, then tin the enamel-coated copper underneath. Without a solder pot it can be done with a generous blob of solder on an iron tip, though that's less controllable.
The strands are enamel coated, so tin the ends by around 5mm before use. The heat burns off the enamel & lets the solder take. Without it you're soldering onto insulation & get no connection. This wire is best suited to someone who's soldered before.