A stitch is a single loop or turn of thread or yarn that is formed by interloping, intralooping or interlacing. Stitches are fundamental for all sewing, knitting, crocheting, embroidery and lace making, regardless if the stitches are crafted by machine or by hand. In most cases of stitch formation, one or multiple needles move through or in between one or more layers of base material (e.g. fabric or leather). When a sequence of consecutive stitches is applied, the resulting row or rows of stitches is often referred to as a stitch line. Stitches are not only used for functional means, they are also applied for decorative purposes. For example, in some cases stitches are applied to incorporate embroidery into a garment, to avoid the edge of a fabric from unravelling or to join two or more layers of fabric together. As there are many different types of stitches, the suitability of a stitch for a given design depends on many factors such as fabric content, seam purpose, design elements and intended end use of the garment. Examples of commonly used stitches are:

• Backstitch
• Chainstitch
• Lockstitch
• Overlock
• Coverstitch

Stitches can be formed via one of three methods:

1. Interloping
   In interloping, a stitch is formed by passing the loop of one sewing thread through the loop of another, separate sewing thread.

2. Intraloping
   In intraloping, the loop of one sewing thread passes through another loop of the same sewing thread.

3. Interlacing
   In interlacing, one sewing thread passes over or around a thread or loop of another sewing thread.

Stitches can be group into different classes based on variables such as the number of needles used, sewing direction, form or shape of the stitch and purpose of the stitch. The classification below shows a commonly used standardization for groups of stitches:

Class 100 – Single Thread Chain Stitch

Class 200 – Hand Stitch

Class 300 – Lock Stitch

Class 400 – Multi-Thread Chain Stitch

Class 500 – Overedge Chain Stitch

Class 600 – Covering Chain Stitch

Most stitches have at least five basic formation steps in common:

1. Penetration of the base material

A needle penetrates the base materials (i.e. fabric, leather, etc.) while carrying the sewing thread.

2. Loop formation

A loop of sewing thread is formed in the scarf of the needle when the needle reached the bottom of a stroke and begins to rise back up again.

3. Conformation

The sewing threads are arranged in their position above, between, around or below the base materials.

4. Casting off

The needle thread loop is released from the lower stitch formation device (e.g. a looper).

5. Setting of the stitch

The sewing thread is drawn into or onto the base materials.

A seam refers to the joining two or more layers of fabric, leather or other base material held together with stitches. Seam are either open (i.e. the seam allowance is visible) or closed (i.e. the seam allowance is incorporated in the finished seam rendering it invisible from the outside). Seams are typically described by their type and structure (e.g. plain seam or lapped seam) and the position on the garment (e.g. shoulder seam or side seam). This means that a seam contains the stitch line or lines used to hold these layers together, as well as the placement and/or folding of the base material to create a specific arrangement of the layer or layers. Example of fundamental seams include:

• Plain seam
• French seam
• Flat seam
• Lapped seam

It is important to know that seams are not always held together by stitches and sometimes glue or other adhesives can be used to create or support a seam as well.

Stitches and seams are closely related. A stitch is a single loop or turn of thread that is created via interloping, intraloping or interlacing. A row of consecutive stitches is referred to as a stitch line. Together with the specific structure of the fabric (e.g. folds and layering), these stitches are among the key elements that make up a seam. Seams are denoted as the connection of two of more layers of fabric by using stitches.