The medium set is a pack of 3 needles, in 3 different sizes. They are appropriate for sport to worsted weight projects.
The fine set is a pack of 6 needles, in 6 different sizes and lengths. It would be appropriate for fingering and lace weight projects.
The thick pack is a set of 3 heavier gauge needles, in 3 different sizes. This set is best suited to worsted to chunky weight projects.