This is a roll of Qian Jin String for winding the nut of an Erhu.
The material used to make the nut of the Erhu affects the tone of the instrument as well as its ability to stay in tune. On sale is the kind of material specially made for this purpose. It is flexible enough to be easily wound round the neck yet strong enough to stay in shape.
One roll is approximately 15 feet long and more than enough to wind 10 Qian Jin.
The way the Qian Jin is wound also affects the sound of the instrument.