Have you ever heard of tailor’s wax? In earlier times, beeswax was used to seal and smoothen the surface of yarns. Today, paraffin does the trick. The yarn is pulled through the notch of the plastic box. A layer of paraffin is then applied to the yarn. A thread treated in this way is much easier to thread and glides better through thicker, more robust fabrics. There is another possible application: If a zipper is stuck, a little tailor’s wax will work wonders. All you have to do is open the small container and take out a piece of paraffin.
Note: Tailor’s wax is intended exclusively for hand sewing, a thread that has already been waxed does not belong in the sewing machine.