Take piece of cardboard or anything else suitable for the length of your tassel. Wrap thread around the cardboard several times. Cut one side, make a knot with an extra thread at the center.

Divide into four braids, knot like shown on the diagram.

Prepare a cord and knot the loose ends. Insert the cord before you tighten the tassel knot. Take a thread and wrap several times around the tassel. Secure end of that thread with a knot and some stitches with a needle. Trim tassel evenly.

Finished!