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Thread weight is a standard by which the weight and thickness of thread can be measured and compared through quantitative means. There are several weight systems, and all of them typically indicate how a certain amount of the thread satisfies a certain weight criteria, allowing different sizes of thread to be compared. The most common systems of measurement are weight, denier and tex, all of which are based on metric measurements.
There are various ways in which thread weight can be indicated on thread packaging, and different methods typically cannot be interchanged without proper conversion. Conversion tables are available, but it usually is easiest for a single standard to be used whenever one is dealing with thread. Also, the way in which thread is labeled can be quite misleading. A spool of thread might read “50 weight” or “50 wt.,” and this is not necessarily the same as “#50” thread.
One of the most common ways of indicating thread weight is through the use of the term “weight” or the abbreviation “wt.” This type of weight typically indicates the length of thread in kilometers that would be necessary to weigh 1 kilogram (2.2 pounds), which means that “weight” on a package is actually an indication of length. Therefore a thread with a thread weight of 50 would require 50 kilometers (about 31 miles) of the thread to weigh 1 kilogram (2.2 lbs). A 30-weight thread would require only 30 kilometers (about 18.6 miles) of the thread to weigh that amount, so a lower number indicates a thicker and heavier thread.
The denier method of thread weight indication is fairly similar, though it uses a set length of thread and indicates the weight of that amount. Specifically, the denier system indicates the weight of the thread, in grams, of 9,000 meters (almost 5.6 miles) of the thread. That length of a 100-weight thread, using the denier system, would weigh 100 grams (0.22 pounds). Therefore, with this system, the higher the thread weight, the heavier the thread.
Similar to the denier method, the tex method indicates the weight in grams of 1,000 meters (about 0.62 miles) of the thread. This means this length of a 40-tex thread weighs 40 grams (about 0.09 pounds). Much like the denier system, a higher number indicates heavier weight and thicker thread.
In any of these systems, a numerical notation often follows the weight to indicate the number of individual threads intertwined to make the thread on the spool. A spool of thread using the denier weight system might read “100/2,” for example. This means that the thread on the spool consists of two threads intertwined together, each having a weight of 100 denier, for a total thread weight of 200 denier.