From the book:
Cover your old bracelets, mailing tubes, or foam can cozies to make these fun to wear bangles. Linked double crochet makes a sturdy fabric, and the variegated sock yarn guarantees that every bracelet will be one-of-a-kind. They’re perfect for quick gifts or to personalize every outfit.

Other supplies: Yarn needle, new or vintage bangle bracelet or plastic or cardboard tube with approximately 3”/7.5 cm diameter and 1”/2.5 cm (or desired) width.