Janome Superlock 634D Serger Sewing Machine with Cloth Carrying Case. What is a serger sewing machine? Cover stitch & serger sewing machines are used to create decorative and professional-looking stitches, hems, and seams. They are great for adding detail and flair to your projects, and can be used on a variety of fabrics. Erger and sewing machine differences. Serger sewing machines use an overlock stitch to create a professional finish, have multiple thread sources for versatility and can cut fabric as they stitch, making them faster than other sewing machines.