Cars are also called sewing machines. When knitted garments are made into ready-made garments, the seams are sewn with hemming. The seams are mostly two or more layers, which makes the seam powder prominent and inconsistent. At this time, it is necessary to cover the wrapping seam with a stretching seam to make the protruding seam fit. Sewing machines, also known as sewing machines, yard sewing machines and bone sewing machines, are generally divided into three lines, four lines and five lines. The main function is generally to prevent pilling in the seams of clothing.