There's is a light fingering and some sock yarns are thinner than another. All the weight classes are a range of yarn thicknesses because it depends on the manufacturer. Knit picks Merino is called a dk when it feels just like a worsted and has the same yarns to gram as worsted. But it's soft and will squish down to a dk gauge and many people say it should be knit tighter because merino stretches a little. So you're going to find heavier or lighter yarns in each weight category.
sue- knitting heretic