Petra Crochet Cotton Thread Size 3. These balls of highly mercerized cotton are lustrous, non-divisible and made of 100% cotton. Perfect for cross stitching, needlepoint and embroidery on a wide variety of fabrics when a rich raised pattern is desired and for the finest of crocheted lace. Size: 3. Length: 306yd (280m). Comes in a variety of colours. Each sold separately. Machine washable, dry clean safe, ironing safe, do not bleach. Dry cleaner safe with P solvents. Imported.