The Sentro 40/48 uses this tension gauge to make sure that the yarn feeds properly to the machine to create the knit stitch. It has three settings: tight tension, medium tension and loose tension. The tension setting depends on the type of yarn you are using with your knitting machine. With this purchase, you will receive two tension gauges. Since they are made of plastic, you must be careful when feeding your yarn. If your yarn has a knot and you do not see it, the tension gauge could bend and possibly break. This product was made by the original manufacturer. It is not a 3D printer creation.