This project uses 6x4 mm aluminium curb chain, worsted weight yarn and a 2.55 mm crochet hook. If you wish to use smaller chain or thinner yarn or even thread, experiment with different size hooks to ensure you can insert the hook into a link to hook up the yarn or thread.
Measure your wrist and cut the chain to the right length after allowing for ease (about 3/4") and the addition of jump rings and a clasp.
You will also need a large hole needle like a tapestry needle for weaving in the ends.
Make a starting slip knot and hook the loop up. If you are new to crochet, check out the first 3 steps shown here