Crochet thread produces fabric of fine gauge that may be stiffened with starch.
Crochet thread is almost always produced from cotton and has a denser pile and smaller diameter than ordinary yarn.
Crochet thread can withstand considerable stresses from pulls with sharp hooks.
Crochet manufacturing conventions treat thread and yarn quite differently: manufacturers designate different sizing scales for thread and yarn.
Smaller sizes (40 and up) are often used for tatting jewelry and fine lace.