Plied yarn means double or folded yarn. If you twist 2 yarns together then you generate two plies and three plies or four plies depending on how many yarns you are twisting
Plied yarn count is denoted n/Ne. The first alphabet is representing how many yarns you are twisting and the second alphabet which is representing the count of the single yarn
Eg. 2/17s is showing the plied yarn consisting of 2 single plies. 2 indicate 2 yarns twisted , and each yarn has a 17s count. S is indicated for English count 17s means 17Ne
If 2/60s yarn is twisted together the Yarn count is ( in Tex )
1/Nr = 1/N1+1/N2
1/60+1/60
Nr=30s
In Tex
Tex=590.5/30=19.68
