Well, Christy, I am checking my spools now. I haven't bought Coats and Clark for many years, because I don't like it in the machines, I find it gives off more fuzz. The ones I have left do not have their size on them. Maybe C&C only makes 50?
Piecing: My Gutermann all have the weights/size on them (C NE 50,) as do Aurifil (GR 30, NE 50/2,) Sulky (30 WT,) Mettler (NE 50/3.)
Hand/machine (?) quilting: YLI (40/3ply,) King Tut (#40,) Gutermann (Quilting,) Mettler (Quilting.)
Hand applique: YLI (Silk #100,) Mettler (Embroidery Ne 60/2.)
So, it may be just the "better" threads (my personal opinion, of course,) that have the sizes and info imprinted on the spool itself.