A surgeon's know it wrapped twice to the left and pulled tight, then wrapped twice to the right and then pulled tight. I do not use heavy yarns, only crochet thread or baby yarn or embroidery floss. Some charities have been scared out by the rumor that they are dangerous to babies, but if they are properly tied I have never lost a single tie. They are certainly appropriate for older children and lap quilts for older people and so far as I know there are no bans on those.