The thread on the left is YLI 60/2 cotton thread. The 60/2 means it's a 60 weight thread and it's made of two pieces of thread twisted together. The thread in the middle is Wonderfil 80 weight Deco-bob. It's shiny and great and very thin. The thread on the far right is Wonderfil 100 weight Invisifil polyester thread. It's very fine and wonderful to work with.
The picture above shows all the different weights I used in this project. 40 is on the left, then 50, then 60, then 80, and finally 100 weight. You can tell the difference in thickness. It will be nice to have a sample to look at when I'm choosing threads for projects!