To the part that holds the loops.
I cut the piece, ironed the edges in and then folded it in half and ironed again.
I ironed a vlieselin on the place for the grommet and prepared a rectangle of a tough canvas. I turned the upper part right sides together and sewed the tip horizontally. I cut the allowance at the corners, inserted the rectangle (to toughten the place for grommet even more) and turned over.
Finishing was as usually - sewing the black piece to the poi and making the loops and the case. This time, I made a long big sack for the sand so that the sand could move in it and I could easily squeeze it in by the narrow hole.
In motion they look beautiful:-)