Aran yarns, which are medium-bulky weight, are perfect for making warm garments and winter accessories like hats and scarves. These Group 4 Medium yarns are worked with 5-6-mm knitting needles or a 6-mm crochet hook. One ball of 100 grams of (10 ply) Worsted weight yarn can consist of between-180 meters. These yarns usually have a WPI (Wraps per Inch) of 8.