What occurs when the lower and upper threads in a sewing machine form a stitch?

When the lower and upper threads in a sewing machine form a stitch, they interlock. This process occurs as the sewing machine needle punctures the fabric, bringing the upper thread down through the fabric and into the bobbin case, where it meets the lower thread coming from the bobbin. The two threads then wrap around each other, creating a secure connection that holds the layers of fabric together.

The interlocking of these threads is crucial for creating a strong and balanced stitch, essential for sewing effectively. This interlocking action contributes not only to the structural integrity of the stitch but also to the overall quality of the finished garment or sewing project. Understanding this mechanism is fundamental for anyone learning to sew, as it helps in troubleshooting issues like skipped stitches or uneven seams.