How Does a Sewing Machine Stitch?

In the most common stitch type — the lockstitch — the needle pushes the upper thread down through the fabric. As the needle rises, a small loop of upper thread forms beneath the fabric. A rotating hook (or shuttle) catches this loop and passes it around the bobbin, which holds the lower thread. The two threads interlock, and the feed dogs advance the fabric for the next stitch. This happens at remarkable speed: industrial sewing machines can make over 5,000 stitches per minute. The tension discs control thread tightness, ensuring stitches are balanced and the interlocking point sits within the fabric layers.