Weaving yarns are described by two numbers separated by a slash, eg 2/5, 3/10, etc.
The smaller number is the number of plies
The larger number represents the size of each ply.
So, a 2/5 yarn has 2 strands of size 5 thread. A 3/10 yarn has 3 strands of size 10 thread. Different sources are inconsistent about which number comes first. Usually the smaller ...