Why are thread weights sometimes listed in pounds (#) and other times listed as a fraction?
The American system of weighting thread is by using a “Tex” system. The Tex system shows the weight of the thread in pounds (#). The larger the number the thicker the thread. For example, an 80# thread would be thicker than a 50# thread.
In Europe, thread weight is measured a different way. They measure the weight in grams of 1000 meters of thread. This is displayed as a fraction. For example, 120/1 would mean that 120m weigh 1-gram.