Twist, twist angle, twist width and twist coefficient are indicators of yarn twisting degree. The index indicating the direction of twisting is called twist direction.
Yarn：
The two cross sections of the yarn produce an angular displacement of 360 degrees, forming a twist, that is to say, a circle.
The number of twists per unit length of yarn is called twist. China’s cotton yarns are twisted by special number, i.e. the twist number within 10 cm yarn length; combed wool yarns and chemical filaments are twisted by metric count, i.e. the number of twists per meter; in addition, there are British count twists expressed by the number of twists per inch.
Twist angle：
Before twisting, the fibers in the yarn are parallel to each other. After twisting, the fibers incline. The bigger the twist degree of yarn is, the bigger the fiber inclination is. At one time, the twist degree can be expressed by the inclination angle β of the fiber in the yarn.
The twisting degree of two yarns with the same twist is different because of the different thickness. The twisting degree of the thicker yarn is larger and the twist angle β is larger.
Twist width：
If the yarn cross section is regarded as a circle, the angle between the fibers and the yarn axis at different radius is different. In order to show this situation, twist width is introduced.