Threads 120/2: decoding of markings and application

When choosing sewing accessories for professional work or home creativity, you can often encounter incomprehensible digital symbols on spools. One of the most common markings is 120/2, which baffles many novice masters. These numbers are not a random set, but represent a strict technical standard that determines the thickness and structure of the thread.

Understanding this marking system is critical to obtaining a high-quality seam, since an incorrectly selected thickness can ruin not only the appearance of the product, but also damage the mechanism of the sewing machine. In this article we will analyze in detail what is hidden behind these numbers, how they affect the sewing process and why this type of thread is considered a universal standard in many light industries.

Once you understand the nomenclature, you can accurately select materials for silk fabrics, synthetics and fine cotton. This knowledge will allow you to avoid problems with thread breaks or, conversely, with excessive thickening of the seam, which is especially important when working with complex delicate materials.

Decoding the numerical designation

To understand what it means 120/2, you need to refer to the numbering system adopted for sewing threads. The first number, in this case 120, indicates the linear density or, more simply, the fineness of the thread itself. The higher this number, the thinner and lighter the thread itself. This may seem counterintuitive at first glance, but in the metric numbering system, the 120 number is significantly thinner than, for example, the popular 40 or 60 number.

The second digit following the fraction indicates the number of additions. The number 2 means that two separate threads (strands) of number 120 are twisted together into the finished thread. If the spool said 120/3, it would mean that the thread was made of three plies, making it thicker and stronger, but maintaining the overall fineness number of the original raw material. It is the number of folds that determines the final thickness of the thread that you see on the spool.

It is important to note that the thread 120/2 considered very thin and light. It is often used where maximum invisibility of the seam is required. Unlike coarser analogues, such threads create virtually no volume at the junction of fabrics, which makes them ideal for hidden hemming or working with transparent materials.

There is also the concept of thread twist, which is not always indicated explicitly in the labeling, but affects strength. For number 120, the twist is usually made dense enough so that two thin threads do not fluff during the sewing process. This ensures the stability of the thread passing through the needle and the shuttle mechanism.

Physical properties and characteristics of the material

Threads marked 120/2 have a unique combination of strength and elasticity, despite their microscopic thickness. Most often they are made from 100% polyester, which makes them highly resistant to tearing and abrasion. The synthetic base also provides resistance to fading and household chemicals, which is important for products that are subject to frequent washing.

One of the key characteristics is low elongation at break. This means that the thread does not stretch as much as an elastic band, but also does not break when the fabric is slightly stretched. This elasticity allows the seam to retain its shape even after repeated deformations of the product. In comparison, cotton threads of the same thickness would be more brittle and less durable.

⚠️ Attention: When working with 120/2 threads, it is extremely important to correctly set the upper thread tension in the sewing machine. Due to the high slipperiness of synthetic fibers, the standard setting may be too strong, causing the fabric to pinch.

The heat resistance of such threads also deserves attention. Polyester can withstand high ironing temperatures, does not melt instantly, like some cheap analogues, and does not shrink. This makes them suitable for products that will be subject to heat treatment during production or care.

The smooth surface of the 120/2 thread reduces friction when passing through the fabric. This property minimizes the risk of damage to the fabric structure, which is especially important when sewing expensive silk or satin materials, where every needle puncture is visible to the naked eye.

Scope of application of thin threads

The main area of application of threads 120/2 - This is a clothing production for light industry, where high precision and aesthetics are required. They are used for sewing thin fabrics such as chiffon, cambric, thin silk and synthetic analogues. In these cases, thicker threads would create undesirable texture and could even cut through delicate fabric.

This type of thread is also widely used for making blind seams and hemming the bottom of products. Thanks to its fineness, the seam becomes almost invisible from the front side. This is especially important when sewing evening dresses, blouses and children's clothing, where comfort and the absence of rough seams play a paramount role.

• 🧵 Bottom hem: Ideal for turning up the edges of trousers, skirts and sleeves where the thread should not show through to the right side.
• 👗 Sewing blouses and shirts: Used for sewing side seams and finishing collars on thin fabrics.
• 🧸 Toys and decor: Used for sewing on small parts, eyes or decorative stitching on miniature items.
• 🧵 Clothes repair: Excellent for darning small holes on delicate fabrics where you need to match the color and structure as accurately as possible.

In home needlework, 120/2 threads can be used for embroidery on thin fabrics or for creating three-dimensional elements that require many layers of thread. However, for ordinary household needs, such as sewing buttons on coats or jeans, they will be too weak and thin.

Table of correspondence between numbers and thickness

To better understand the place of 120/2 threads in the general numbering system, it is useful to consider the comparative table. It shows how the thickness of the thread changes depending on the number and number of folds. This will help you visualize the differences between the different types of reels you might find in a store.

As can be seen from the table, the transition from number 80 to number 120 marks the entry into the zone of ultra-fine work. If the 80th number can still be used for regular machine stitching on light fabrics, then the 120th number already requires a certain skill and suitable equipment. The difference in thickness between 80/2 and 120/2 is significant, although both threads appear very thin.

It is worth considering that different manufacturers may have slight deviations in the actual thickness of the thread, even with the same markings. Therefore, for critical work, it is better to first test the coil on a piece of fabric to ensure the expected result.

Compatible with needles and equipment

Working with threads 120/2 requires appropriate equipment for the sewing area. First of all, this concerns the choice of needle. For such a thin thread, standard #90 or #100 needles will be too large, as a large eye can damage the thread structure or create unnecessary friction. The optimal choice would be needles No. 60, No. 65 or maximum No. 70.

Using the wrong needle can cause the thin thread to wander around in the eye, causing skipped stitches or breaks. In addition, a needle that is too thick will leave noticeable punctures in thin fabric, which will negate all the benefits of using micron thread. The needle must be sharp (Sharps type) or universal, but always thin.

Threading the thread into the machine can also be difficult due to its thinness. The 120/2 thread is very light and can frizz, so it is important to ensure that it fits correctly into the tensioner and does not get tangled in the guides. It is recommended to use thread mesh on the spool to prevent the threads from slipping and unwinding too much.

⚠️ Attention: Never use 120/2 threads in overlockers unless it is provided for in the instructions for a specific model. For overlockers, special conical threads of a different twist structure are usually used.

If your sewing machine has automatic threading, make sure the mechanism is designed to handle fine numbers. In some cases, it is easier to thread a thin thread by hand, using a special threader or simply cutting the end of the thread at an acute angle.

Tips for handling and storage

To achieve the best results when using 120/2 thread, a number of technical recommendations must be followed. Firstly, the length of the thread threaded into the needle should not be too long. Due to the thinness and slipperiness of polyester, the long tail may slip out of the needle after the first stitches, and the process will have to start all over again.

Secondly, it is important to monitor the quality of the thread itself on the spool. There should be no knots, thickening or tears on it. Since the thread is thin, any defect may cause sewing to stop. Before you begin, run your finger over the thread to make sure it is smooth and even.

Storing such threads also has its own characteristics. They should be kept in a dry place, away from direct sunlight. Polyester is UV resistant, but prolonged exposure may change its color or make the thread more brittle over time. It is best to keep your spools in closed boxes or organizers.