These threads are supplied as an 80m ball and are 3-ply which is half the width of the ordinary 20m ones. The colours correspond to their 20m, 6-ply counterparts. So you can use them to add fine details and accents to your projects, alongside the 20m threads of the same colour.
At first glance these fine sashiko threads look quite similar to perle thread, however perle has a sheen whereas sashiko thread is matte. Perle is also 2-ply rather than 3. With these, you know you are getting the real deal, authentic product from Japan rather than 'making do' with something that isn't quite right.
Of course, if you don't want to buy the 20m and fine versions of the same colour, you could always stitch with the fine thread doubled. This will give you the same thickness as the 20m thread, although the effect will be slightly different as the threads will lie alongside each other rather than be one thread. This is still very much in the tradition of sashiko, though!
These threads are so cute, the labels on the packets were even designed to make them look like 'mochi' rice cakes!