Stitch Per Inch: Meaning and Types

When sewing clothing, there are other options to take into account besides the fabric and pattern you choose. Not only do stitches affect seam strength, flexibility, and attractiveness, but they also have a big impact on how long sewing cycles take and how much it costs to produce an item. In some cases, lock stitching may be required. In some cases, a mix of lock stitching and overlock stitches is required. Whatever the combination, the quality and price of your order will ultimately depend on these choices and the stitching characteristics that you want.

You’ll be able to assess your clothing more carefully during product inspection at the factory if you are familiar with these four basic stitches and how to evaluate each one. Additionally, you’ll be in a better position to provide your customers with the goods they desire and keep up with the most recent fashion trends. Last but not least, this gives you more control over the final output to avoid quality problems.

Meaning of Stitch Per Inch (SPI)

The meaning of stitches per inch is straightforward. You can find out how many stitches are in one inch by changing the setting. There are 15 stitches in an inch if the setting is 15. The meaning of metric settings like 2.5 is a little less clear. They speak of the measurement of each stitch. If the setting is 2.5, then each stitch will measure 2.5 millimetres in length.

By noting the number of stitches per inch (SPI) on a piece of clothing or group of garments, you can get a general indication of the length and quality of the stitching. Greater stitch density and frequently higher stitch quality are indicated by a higher SPI. Usually, more short stitches indicate stronger seam connections.

Sometimes, more ornate designs also require a higher SPI. On the other hand, a lower SPI frequently denotes inferior quality. Low-SPI garments frequently feature long stitches, are less resilient, and are more likely to snag. Low-SPI garment stitching takes less thread, which is its main benefit. As a result, manufacturing clothing with a lower SPI is frequently quicker and less expensive. A higher SPI will normally require more time and thread, which could raise your manufacturing costs.

Types of Sewing Stitches

A taxonomy for stitches called ASTM D 6193 was developed by the American Society for Testing and Materials (ASTM) in response to the great range of stitches used in the production of clothing. A classification scheme developed by the International Organization for Standardization (ISO) is called ISO 4915:1991. The grouping used by ASTM will be used interchangeably for the remainder of this essay. Each common stitch type is divided into classes of “100,” “200,” “300,” and so on. Within that group, different stitch kinds are further defined by their digit endings.

Lockstitch

The class 300 lockstitch, also referred to as single-needle stitching, is created when two threads lock together intermittently. It happens when a needle thread loop that is going around the bobbin and tying two threads together is caught by a rotary hook. Due to its ease of use and low cost, this stitch is quite popular.

Overlock Stitch

Other names for the class 500 overlock stitch include overedge, overlock, serge, overcast, and merrow. It is frequently applied in the sewing method known as “over-sewing,” which involves forming a stitch over the edge of cut fabric. The very flexible overlock stitch is frequently employed to finish the edges of knitted materials.

Chain Stitch

A chain-like pattern is formed when two or more sets of threads are woven together to form the chain stitch, which belongs to class 100. The substance being utilised is penetrated by one or more needle threads, which then create a loop there. Chain stitching is commonly used on clothing’s decorative elements and other places where some work may improve aesthetics.

Chain Stitch with Multiple Threads

The double-locked chain stitch, often known as the multithread chain stitch, belongs to class 400. It develops when one or more needle threads pass through the cloth and interlock with a collection of looping threads on the garment’s bottom. The multithread chain stitch, when properly executed, is less prone to seam puckering because it lies beneath the fabric rather than between its layers.

Indicators of SPI

It includes −

Seam Strength

These qualities work together to increase a garment’s seam strength. To calculate how much pressure a seam can withstand before breaking, typical stitches particularly use SPI. This information is crucial since it enables quantitative measurement-based pass/fail testing of your clothing during inspection. The following two popular sewing stitches used in manufacturing have estimated seam strength formulas:

$$\mathrm{Multithread\:chain \:stitch:\:SPI\:\times\: thread \:strength\: (lbs)\: \times\: 1.7 = seam\:strength \:(lbs)}$$

$$\mathrm{Lockstitch:\:SPI \times\:thread\:strength\:(lbs)\: \times\: 1.5 = seam\:strength\:(lbs)}$$

Using this formula, you can design your garment so that it has the desired seam strength. For instance, a silk scarf might not require strong seams. But for construction work gloves to be useful, a stronger seam is typically needed. For your garments to live up to client expectations, it helps to have an understanding of the stitching qualities and seam strength you desire.

Width, Depth, Consistency, and Tension of the Stitches

The stitch width and depth should be taken into account by garment producers in addition to the length indicators provided by SPI. The distance between the lines of the outermost portions of the stitches is known as the stitch width. The distance between the upper and lower surfaces of a stitch is known as its stitch depth. Stitch consistency, which is the regularity with which each stitch is made in a row of stitches, is crucial for a garment’s structural integrity as well as its aesthetic appeal. Luxury clothing places great importance on consistency. When a factory worker sews a garment incorrectly, that irregularity may also result in a weak spot in the garment’s seam.

The balance of stress on the strands that will eventually form the stitch is known as "thread tension." Excessive tension can cause unbalanced stitch formation, uneven stitches, and seam puckering. Lack of tension might result in looping too much and loose, uneven stitches. Seams can become misshaped or prone to unravelling if there is insufficient tension.

Conclusion

You can see how crucial it is to include details for stitches per inch in your garment specification guidelines from the comments and information mentioned above. For a particular fabric type and application, using the right number of stitches per inch can significantly improve the strength, appearance, and functionality of the seam.