Based on the direction of grains placed in helical curve while twisting the yarn we distinguish the counter-clockwise twist (S) and clockwise twist (Z). Clockwise twist is more usual in single yarns. A number of twists per one meter is usually stated after the letter Z .
Clockwise Twist is also used for permanent twist in which the grains in yarn or roving are twisted several times around the product's longitudinal axis by 360°. Twisting of the yarn or roving is characterized by the number of twists per meter. This type of twist provides a product with better strength than the counter-clockwise twist created by rounding.