Are you talking about Wonder-under, or something like a twill hem tape? I'm not sure twill tape would work on T-shirts. They are stretchy and twill tape is not. If they are woven fabric, it might work, but your best bet would be to find a friend or family member with a sewing machine who can hem them up for you. It is not difficult to do in most cases. Figure out where you want the shirt's finished edge to be, mark it, then cut it about 3/4 inch longer than that. Fold it up twice to meet the finished edge mark, iron it to make it stay, and then stitch it down along the edge. I have used Wonder-under for a few things, and find that it starts to come undone after a few washes, and I am constantly re-ironing it to try to make it stay. Maybe on rarely-worn items it would work better.