1. Направление крутки S-крутка, левая Z – крутка, правая
Show s- and z-twisted thread
Hold the thread vertically in front of you and untwist it
Compare with picture
Why two kinds of twist direction?  for industrial production always z-twisted thread, because it untwists less while sewing
History
For 2-Needle-Machines one s- and one z-twisted thread was used, but danger of mix-up
Today special needle for this problem
Single ply = yarn
Final thread = thread
S-twisted
only for handsewing (steering wheel), mostly waxed
has to do with movement of the hand, to avoid untwisting of the thread
Strongfil 11/2 S, Serabraid for handsewing
Z-twisted
Mostly used for machine sewing thread, because of movement of hook
Single yarns s-twisted, final thread z-twisted, otherwise the thread would curl up  like a gimp/string/cord (Kordel)
S-крутка, левая
Z – крутка, правая

2. Количество слоев 2- слоя 3-слоя 4- слоя Z S Z S Z S 2-fach
Often for sewing units
3-fach
Often for thick threads
More breaking strength
Was usual for threads in former times
AMANN GROUP 2010