ISO 2:1973 Textiles — Designation of the direction of twist in yarns and related products

The direction of twist designation for yarns, complicated yarns, rovings, slivers, slubbings, cordage, and related items is standardized globally under ISO 2.

The direction of twists is indicated by the capital letters S and Z in the standard, as indicated by the slanting direction of these two letters’ centres. The direction in which the twists move away from an observer is known as the handedness of the twist. It follows that Z-twist is seen as right-handed and S-twist is left-handed. By 1957, the cordage industry had adopted the practice of utilizing these two characters to clearly indicate twist orientation.

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