I crocheted the red Openwork Round Motif with cotton thread size 10 and a 1,75 mm crochet hook and its size is 10 cm (about 4 inches) in diameter. For the yellow one I used cotton thread size 5 and a 2 mm crochet hook and it measures 12 cm (4,7 inches) in diameter.
Besides your chosen thread and crochet hook, you will also need a needle to weave in loose ends and a pair of scissors.