The double-needle sewing machine has two needles and two thread spools, while the stitch is created simultaneously on both sides of the fabric. This results in an extremely durable and professional stitch that is not easy to come undone or wear out.
The serger sewing machine uses four threads to create various types of stitches, including overlock stitches, finishing stitches, and others. It is more specialized than basic sewing machines and is usually used by professionals.