Aunt Lydia's Fine Crochet Thread. If you want to make heirloom quality crochet projects reach for Aunt Lydia's Fine Crochet Thread. This 100% mercerized thread is a size 20. It is ideal for crochet projects such as doilies, table runners, holiday decorations, home decor and accessories. The crochet gauge is 46-52 dc =4in (10cm). 100% mercerized cotton. Size 20. 400 yards. Machine wash gentle, roll in a towel and block to dry. Do not bleach, do not dry clean, do not iron.