Using the correct bobbin class (e.g., Class 15, Class 15J, Class 66) is critical for stitch quality. An incorrect bobbin can cause tension problems, skipped stitches, thread jams, and can even damage the bobbin case of your sewing machine.

The required bobbin class for your machine is listed in your SINGER® sewing machine's instruction manual. You can also find this information on the product page for your machine model on the SINGER® website.

No, you should only use clear, plastic SINGER® bobbins in machines with a top drop-in bobbin system. The system is designed to work with the lightweight plastic bobbins, and using a metal one can interfere with the bobbin sensor and affect stitch quality.

While they look very similar, a Class 15 bobbin is flat on the top and bottom, whereas a Class 15J bobbin has a slight curve, making it fractionally shorter. They are not interchangeable, so be sure to use the specific class required for your machine.

One of the main advantages of a top drop-in bobbin system is the clear cover plate. This allows you to easily see how much thread is left on the bobbin at a glance, so you won't run out of thread unexpectedly in the middle of a seam.