Linear density specifications for sewing and embroidery threads

According to the global standard, the linear densities of sewing and embroidery threads are expressed in Tex. At the same time, linear density is still often given in Nm. This is because the ticket numbers of sewing and embroidery threads are based on this length system, and many technicians are still more familiar with it.

In practice, however, two different indications are used: either the final linear density or the single linear density. In order to compare sewing threads, it is important to know the number of plies. Ideally, the ply is stated together with the linear density:

• In the Tex system, this is indicated using a multiplication sign and the corresponding number of plies, for example 10 tex × 3. This means that the sewing thread consists of three yarns, each with a linear density of 10 tex. The resulting total linear density is 30 tex (1,000 m of a single yarn weigh 10 g; 1,000 m of the thread weigh 30 g).
• In the Nm system, this is indicated using a slash and the corresponding number of plies, for example Nm 120/3. This means that the sewing thread consists of three yarns, each with a linear density of Nm 120. The resulting total linear density is Nm 40 (1 g of a single yarn has a length of 120 m; 1 g of the thread is 40 m long).

Please refer to following examples: 

For better understanding, and in view of the development of new sewing thread constructions, the optical diameter of sewing and embroidery threads is often measured in millimetres. This is carried out using a microscope and indicates, as the name suggests, the visible thickness of a thread.

Due to the construction of the sewing thread and the density of the raw material, the optical diameter may vary even within the same numbering. Based on experience, a continuous filament thread of Nm 120/3 appears thinner than a spun thread of Nm 120/3.