How do you tell the weight of thread? Seams like I look for the weight of some threads and it must be hidden in code...or perhaps I need a magnifing glass? Is higher the weight the thinner the thread? Does it change between mfgs?

here is some info from emblibrary---

What is thread weight?
Thread weight indicates the thickness of the embroidery thread. The higher the weight, the thinner the thread. For example, 60 weight thread is thinner than 40 weight.

Regardless of what material they are made of, 40-wt. is the most common weight used in machine embroidery. Most stock designs are digitized for 40 weight thread. Lighter weight, or shall I say thinner weight, threads can be used in designs that are turning out heavier than desired. Using lighter weight thread (50, 60 or 70 weight.) in the fill areas essentially lessens the density in the design, thus making the entire design lighter. Lighter weight thread may also be used for small lettering to help open up small areas in the type.

Heavier thread like 30 weight can be used when you want a redwork or line design to really pop out. However, I would not recommend using thread heavier than the normal 40 wt. for other types of embroidery designs. Using a heavier thread can cause the embroidery designs to be too dense, making them "bulletproof" and possibly even breaking your needle.