There are many types of thread or yarn. In general, the more strands used, the thicker and stronger the thread. Twisting two or more strands together in order to create a thread is called plying. In textile terminology, a single strand or thread that is spun in an anti-clockwise direction is called s-spun. If it is spun in a clockwise direction it is called z-spun. When two or more strands are plied together in an anti-clockwise direction, the resulting thread is called S-plied. If done so in a clockwise direction, it is called Z-plied. Generally s-spun strands are Z-plied, and z-spun strands are S-plied.
There is also another system, the slash system, which is associated with the American textile historian, Louisa Bellinger. The slash system uses a / for an S-spun thread and a \ for a Z-spun thread (for instance, 1/,2\ is a Z-plied yarn made of two S-spun threads). The main problem with this system is that it is hard to define complex thread constructions with multiple plied threads.
See also: thread count
Source: BURNHAM, Dorothy (1980). Warp and Weft. A Textile Technology, Toronto: Royal Ontario Museum, p. 151.
Digital source of illustration (retrieved 8 July 2016).
GVE