Aunt Lydia's Extra Fine Crochet Thread is 100% mercerized cotton size 30 crochet thread. This crochet thread is ideal for fine heirloom quality crochet projects including doilies, table runners, home decor and accessories. Suggested crochet hook: 12. 100% mercerized cotton. Size 30. 500 yards. Dyelotted. Machine wash and dry.