There was a recent post by someone looking for a 30wt thread and responses that we never heard of it, or that it seemed like an awfully thick thread for the application she was going to use it for.
Well, I actually found two spools of 30wt 2 ply in my thread box today when I was looking for the right color to quilt with. Note: I'm not "married" to any thread manufacturer or weight or anything - I have a smorgasbord of thread in my box.
I pulled both of these 30wt spools - both are made by Sulky. One just says 30wt mercerized cotton, the other says 30wt blendable long stiple cotton. Both are two ply.
They feel and look so DIFFERENT in weight and thickness.
I've also noticed this with 50wt from different manufacturers - Gutterman is much thinner than Essential from CT - both are 2 ply. I've noticed differences in others as well.
So ... can I REALLY trust the weight of the thread? Apparently not.