Thread tension is one of the most important aspects of successful sewing. The correct tension will result in even stitches that are the same size and shape. If the tension is too loose, the stitches will be larger and have a more open appearance. If the tension is too tight, the stitches will be smaller and tighter. There also may be skipped stitches or uneven stitching if the tension is not set correctly.
The best way to determine correct thread tension is to sew a test seam on a scrap piece of fabric before beginning your project. Sew a few inches using the stitch length and width you plan to use on your project. Then, carefully examine your stitches. They should be uniform in size and shape with no skipped stitches or other irregularities. Once you have determined that your machine is sewing with the correct tension, you can begin your project confident that your stitches will turn out beautifully!