The lower the number of the thread size the thicker the thread. The higher the number on the thread size - the finer the thread.
Ex: IL020 linen has thread size 30 both warp and weft. So this will be a very fine, thin thread that is used to weave this cloth.
4C22 has thread size 11.6 warp and weft - so you know that this will be a thicker thread used in making of this fabric.