We do not currently know of any antonyms for tassel.
The noun tassel is defined as:
A ball-shaped bunch of plaited or otherwise entangled threads from which at one end protrudes a cord on which the tassel is hung, and which may have loose, danglingthreads at the other end. Tassels are normally decorative elements, and as such one often finds them attached, usually along the bottom hem, to garments, curtains or other hangings.